"And you're sure it's happening today? No over-shot?" Martha enquires as she pokes at her quiver of arrows.

The taxi takes another turn. I shift awkwardly, stuck in the middle. My leg brushes against the Doctor and I can't stop myself from nudging his foot with mine. Our eyes meet. He smiles. "Yep. Doublechecked, triple-checked, quadruple-checked. I say we've got—" Leaning over between the seats, he peers at the digital clock set into the car radio. The driver gives him an odd look when he goes slack-jawed, slowly lowering himself back.

I raise an eyebrow. "We're late, aren't we?"

"No. No, we're perfectly... twenty-two minutes early. And fifteen seconds. Fourteen seconds, now."

"Oh my God! We're gonna miss it."

The taxi comes to a stop. Fishing around in our pockets, we come up with enough for the fare and clamber out. Several pedestrians in the high street stare at us as we unload our archery bows.

"Hang on, which way is it again?"

Martha grabs our attention, pointing to a street sign. "Richmond Park, this way. You know, I could really deal with a better phone. All this travelling is brilliant but I can't even call home."

"You sure it's this way? Only, I could've sworn—"

"Doctor! Doctor!" A girl races out of a bookshop just behind us. Sure enough, she comes right up to us, her golden locks whipping at her face in her hurry. She looks him over, bright-eyed with excitement. "Doctor!"

He hesitates, glancing over at us and back to her. "Hello. Sorry, bit of a rush. There's a sort of... thing happening, fairly important we stop it."

Her lips part with a soft gasp. "My God, it's you. It really is you. Oh, you don't remember me, do you?"

Smiling apologetically, Martha beckons for him. "Doctor, we haven't got time for this. Migration's started."

"Look, sorry, I've got a bit of a complex life. Things don't always happen to me in quite the right order. Gets confusing. Especially weddings. I'm rubbish at weddings, especially my own."

She doesn't seem surprised in the slightest. "Oh my God, of course! You're a time traveller, it hasn't happened to you yet, none of it. It's still in your future."

"What hasn't happened?"

I'm a little surprised he's even asking that. Martha heads back over, tugging on his sleeve to grab his attention. "Doctor! Twenty minutes to red hatching."

A smile of realisation dawns on the girl's face. "It was me," she murmurs. "Oh, for God's sake, it was me all along. You got it all from me."

Hearing the slight rustle of the folder in her hands, his gaze darts down to it. "Got what?"

"Okay. Listen. One day you're going to get stuck in 1969," she explains. The folder is pushed towards him. "Make sure you've got this with you. You're gonna need it."

Now it's my turn to sigh impatiently. "Doctor, come on."

He winces, stuffing the folder inside his jacket pocket. "Yeah, listen, got to dash. Things happening. Well, four things. Well, four things and a lizard."

"Okay. No worries, on you go. See you around someday."

We only move a few steps before he turns again, asking, "What was your name?"

"Sally Sparrow."

"Good to meet you, Sally Sparrow."

A man heading back from the corner shop stops in his tracks. He blinks at us, almost dropping his bottle of milk. Sally takes his hand in hers. Whoever they are, it must mean a great deal more than just a handhold. I've grown quite familiar with the exact look on his face for it not to be.

"Goodbye, Doctor."

——————

"There we go! Universal roaming. Never have to worry about a signal again," the Doctor cheerfully explains.

Catching her phone, Martha examines it with a look of disbelief. "No way! It's too mad. You're telling me I can phone anyone, anywhere in space and time on my mobile?"

"Long as you know the area code. Frequent flyer's privilege. Go on, try it."

She doesn't get a chance. The Tardis jolts, the console flashing a deep red. I grab the screen and swing it around to myself. "Maroon distress signal."

"Locking on. Might be a bit of—" one final tremor knocks us to the ground. The Doctor peers sheepishly over the console at us. "—turbulence. Sorry. Come on, Martha! Let's take a look."

We step out into what looks like the boiler room of a ship. Pipes tangle around us, lining the walls and metal pillars. Steam clouds our vision and immediately turns to condensation on the Tardis windows and our already-clammy foreheads. The Doctor whistles. "Wow! Not that is hot."

"It's like a sauna in here."

"Automated distress signal transmitting," an automated voice announces from muffled speakers.

Leaning over to examine the plumes of steam hissing out of grating between the pipes, he notes, "Venting systems. Working at full pelt, trying to cool down... wherever it is we are. Well, if you can't stand the heat."

He opens up a door at the end of the long, narrow room and we hurry out.

"Oi, you lot!" a voice yells. Three strangers come pelting down the corridor, all grimy and dressed in boiler suits that have been stripped down to accommodate the heat.

"Get out of there!"

"Close that door!"

One of them, a young woman, her honey-blonde hair plastered to her face with sweat, glares around at us. "Who are you? What're you doing on my ship?"

The man who pushes past us to shut the door scrutinises 1our civilian clothes. "Are you police?"

"Why would we be police?"

"We got your distress signal," Martha explains.

I look around at their exhausted expressions and our surroundings. A yellow haze is formed in the air by the sheer heat and warm lighting from an unknown source. "Is something wrong with your venting systems?"

"Better yet," the Doctor adds, "if this is a ship, why can't I hear any engines?"

Pausing, I listen out. He's right. There is no hum, no vibration under our feet. Nothing.

"It went dead four minutes ago."

Another of the men sighs impatiently, "So maybe we should stop chatting and get to engingeering. Captain?"

She doesn't move. An alarm blares overhead. "Secure Closure active," the ship's computer announces.

It comes as a surprise even to them. They wheel around, bewildered. "What?"

"The ship's gone mad!"

Down the corridor, a girl runs in our direction. She ducks under a door just as it starts to close. "Who activated Secure Closure? I nearly got locked into Area Twenty-Seven!" Coming to a stop, she looks around at us, her frustration faltering. "Who are you?"

"He's the Doctor, she's Inara and I'm Martha. Hello." Martha barely seems to notice her, though. Her eyes are far-off and distracted. She approaches a small window behind the others.

"Impact projection. Forty-two minutes, twenty-seven seconds."

"We'll get out of this. I promise."

"Doctor?"

He looks at the Captain instead. "Forty-two minutes until what?"

"Doctor!"

Hearing the rising panic in her voice, we run to the window. Now I see where the light comes from. A blur of amber light blazes outside, an orb far too big for us to see its full shape. Just the sight of it stings my eyes.

"Forty-two minutes until we crash into the sun."

He sprints back, shaking the Captain urgently by her shoulders. "How many crew members on board?"

"Seven, including us."

"We transport cargo across the galaxy. Everything's automated. We just—"

He's off again before the engineer can finish explaining. "Call the others. I'll get you out."

"What's he doing?"

"Doctor, don't!"

Their warnings come too late. The second he opens the door again, a cloud of burning hot steam bursts out at him. He is knocked back, cradling his burnt hands. Martha and I rush to his aid, while the others bolt the door shut again. "But my ship's in there!"

The younger man stares down at us in confusion. "In the vent chamber?"

"It's our lifeboat!" he protests.

"It's lava."

Pulling her heat-proof gloves and welding mask off again, the girl points to a dial on the wall. "The temperature's going mad in there. Up three thousand degrees in ten seconds and still rising."

"Channelling the air. The closer we get to the sun, the hotter that room'll get."

Martha seethes, glaring at the door as if she might burn through it to the Tardis with pure willpower. "We're stuck here!"

He shakes his head insistently. "So, we fix the engines, we steer the ship away from the sun. Simple! Engineering down here, is it?"

"Impact in 40.26."

We follow him down a narrow passage and a step ladder into their base, stumbling over loose equipment and ducking under pipes. "Blimey! Do you always leave things in such a mess?"

They seem just as shocked when we reach the engine. Rubber tubing hangs loose, leaking liquids that I'm certain should not be uncontained. "It's wrecked!"

I carefully take hold of a section of a hanging tube, squinting down at it. "That's been melted apart. Efficient, I'll give them that."

"Someone knew what they were doing."

"Where's Korwin? Has anyone heard from him or Ashton?" the Captain asks.

"No."

Still caught up on the destroyed engine, Martha follows our investigation. "You mean someone did this on purpose?"

The Captain heads over to an intercom panel in the corner, activating the microphone. "Korwin, Ashton, where are you?" The others go quiet. Nothing comes in reply. "Korwin, can you answer?" Again, nothing. "Where the hell is he? He should be up here!"

Peering at a small screen, the Doctor prods his glasses up the bridge of his nose. "Oh, we're in the Torajii system, lovely! You're a long way from home, Martha. Half a universe away."

"Yeah, feels it."

"And you're still using energy scoops for fusion. Hasn't that been outlawed yet?"

She shares a glance with one of the engineers, one that clearly shows that they are both well aware by the guilty lowering of his head. "We're due to upgrade next docking. Scannell, engine report."

The older one, in his early forties with a patchy beard, brushes past us to get to the computers. Whichever button he presses only causes a beep of refusal. "No response."

"What?"

He jogs over to another machine covered with tubes and wiring. "They're burnt out. The controls are wrecked, I can't get them back online."

The Doctor scoffs, tearing his glasses off again. "Oh, come on. Auxiliary engines! Every craft's got auxiliaries!"

"We don't have access from here. The auxiliary controls are in the front of the ship."

I frown. "No shortcut? No bypass? Nothing?"

"Nothing. All at the front with twenty-nine password-sealed doors between us and them. We'll never get there in time."

"Who in Minerva's name built this ship? Because I'll be having words!"

Looking around at them, Martha suggests, "Can't you override the doors?"

Scannell shakes his head. "No. 'Sealed Closure' says what it means. They're all deadlock sealed."

"So a sonic screwdriver's no use."

"Nothing's any use! We've got no engines, no time and no chance."

The Doctor quickly grows impatient with his complaining. "Oh, listen to you, defeated before you've even started! Where's your Dunkirk spirit? Who's got the door passwords?"

Shrugging, the younger engineer awkwardly nods to one of the doors. "They're randomly generated. Reckon I'd know most of them. Sorry, Riley Vashtee."

"What are you waiting for, Riley Vashtee? Get on it."

"It's a two-person job. One to take this for the questions, the other to carry this," he says, taking a large and heavy-looking duffel bag full of tools from a hook on the wall. "The oldest and cheapest security system around."

The Captain quirks an eyebrow. "Reliable and simple. Just like you, eh, Riley?"

"Try to be helpful, get abuse. Nice."

Martha sighs and takes one of the bags from him. "I'll help you. Make myself useful."

"It's remotely controlled by the computer panel. That's why it needs two."

I manage to pat her on the back as they head off, and the Doctor forces a smile. "Oi, be careful."

"You too."

The intercom beeps. "McDonnell, it's Ashton."

Wasting no time, the Captain rushes back over. "Where are you? Is Korwin with you?"

We exchange wary glances. Whoever this Korwin person in, they're important to her.

"Get up to the Medcentre, now!"

—

"Impact in 36.50."

We follow the sound of shouting. An engineer and a woman in medical scrubs struggle to hold someone down, forcing him into what looks like some kind of cylindrical stasis chamber. The Captain zeroes in on the patient, her panic only growing when she hears his pained cries. "Korwin! What's happened, Abi? Is he okay?"

"Kath, help me! It's burning me!"

We join them in holding him down. I stare at his writhing form, his eyes clamped tightly shut. His skin is reddened and beaded with sweat, peeling and blistered in places. "How long's he been like this?"

"Ashton just brought him in."

He tries to sit up again but we push him onto his back. The Doctor starts to scan his face with the sonic. Immediately, I throw out an arm to keep Captain McDonnell back. "What are you doing?" she indignantly protests.

"Don't get too close," Ashton — a bald, older man dressed in the same boiler suit as the rest of the engineers — pleads, joining my attempts to stop her from interfering.

"Don't be stupid, he's my husband!"

"And he's just sabotaged our ship."

Her movements slow. "What?"

"He went mad. He locked the ship, then he sent a heat pulse to melt the controls."

She blinks. Without hesitation, her focus returns to comforting her husband, supporting his head. "He wouldn't do that!"

"I saw it, Captain."

The Doctor breaks up the argument, gently tapping the patient's shoulder and calling out, "Korwin? Korwin, open your eyes for me a second?"

He thrashes, desperate to get free. "I can't!"

"Yeah, 'course you can. Go on."

Still, he doesn't. "Don't make me look at you. Please!"

I grab a syringe gun from the trolley beside us and prep it with a vial of sedative. "All right, Korwin, hold still. This'll hurt but it'll help a bit. And Gods damn me if I'm not perfectly honest, yeah?"

"Y-Yeah."

"Here we go."

I press it against his neck and pull the trigger. He tenses, groans, and goes limp. Just a second of contact with the skin on his neck is enough for me to recoil. He's burning hot. Resting a hand on his chest to feel its steadier rise and fall, seemingly unbothered, the Captain takes a deep breath. "What's wrong with him?"

The Doctor shrugs, leaning against the flatbed that juts out of the cylindrical. metal chamber. "Rising body temperature, unusual energy readings..." He snaps his fingers. "Stasis chamber! I do love a good stasis chamber! Keep him sedated in there, regulate the body temperature. And, just for fun, run a bio-scan, a tissue profile and a metabolic detail."

Abi eyes him suspiciously over her shoulder as she returns to a screen on the side of the chamber. She tucks a few loose curls that have fallen from her bun behind her ear. "Just doing them now."

"Ooh, you're good! Anyone else presenting these symptoms?" he asks.

"Not so far."

"Well, that's something."

The Captain shifts impatiently, not taking her eyes off Korwin for a second. "What's the matter with him?"

"Some sort of infection. We'll know more after the test results. Now, allons-y, back downstairs. Eh? See about those engines, go." Ashton obeys but she doesn't move, still watching him. "Hey, go."

I offer a reassuring smile. "It'll be okay."

While I expect us to stay, I am moved on by a tug on my arm. The Doctor shouts back to the medic over his shoulder. "Call us if there's news. Any questions?"

"Yeah. Who are you?"

"That's Inara. I'm the Doctor."

—

"Impact in 32.50."

"Abi, how's Korwin doing? Any results from the bio-scan?" the Doctor asks over the intercom. I stand beside him, rifling through toolboxes and loose engine components in search of something, anything, to save us.

"He's under heavy sedation. I'm just trying to make sense of this data. Give me a couple of minutes and I'll let you know."

He returns to the wrecked engine and I take my turn, impatiently prodding the button for the microphone. "Martha, please tell me you're hearing this. How are you doing?"

"Area Twenty-Nine, at the door to Twenty-Eight."

Sprinting back, he puts his glasses on to examine the countdown at the top of the screen. Just over half an hour left. "Yeah, you've got to move faster."

"We're doing our best."

A series of beeps can be heard from the other side and Riley recites, "'Find the next number in the sequence: 313, 331, 367.' What?"

She laughs nervously. "You said the crew knew all the answers."

"The crew's changed since we set the questions."

"You're joking."

The Doctor looks up from soldering a couple of loose wires together. "379?"

Martha pauses. "What?"

"It's a sequence of happy primes. 379," he explains.

"'Happy' what?"

"Just enter it!"

Still, they hesitate. "Are you sure?" Riley asks after a second. "We only get one chance."

The glasses come on again. In any other situation, I'd laugh. "Any number that reduces to one when you take the sum of the squares of its digits and continue iterating until it yields one is a happy number. Any one that doesn't isn't. A happy prime is a number that is both happy and prime. Now type it in! I don't know, talk about dumbing down. Don't they teach recreational mathematics anymore?"

Raising an eyebrow, I tease, "See, most people find it obscene for the words 'recreational' and 'mathematics' to even be spoken in the same sentence."

"We're through!"

"Keep moving, fast as you can. And Martha, be careful. There may be something else on board the ship."

He takes a moment to wipe the mist from his glasses, smiling when she replies, "Any time you wanna unnerve me, feel free."

"Will do, thanks."

"Impact in 30.50."

Returning to the engine, I get down on the dolly and push myself under. My hand emerges a second later, closing around thin air. "Spanner."

One is dropped into my palm and I grin as a pair of Converse trainers pass behind my head. He potters around above me and hands down equipment whenever I ask. I squint up at the mess of metal that hangs over me, most of it designed in a way that I haven't seen since my early days as a Time Agent in training. The heat mixed with the engine grease makes my eyes sting painfully but I power through, grateful for the welding mask I am given to shield my face.

It doesn't take long for me to give up. "I'm sorry. I just can't figure this thing out."

"We need a backup in case they don't reach the auxiliary engines in time. Come on, think! Resources! What have we got?"

"Doctor?"

He huffs, although I imagine he is relieved to hear that Martha is still all right. "What is it now?"

"Who had the most number ones, Elvis or the Beatles? That's pre-downloads."

Hauling myself up to my feet, I toss away the mask and watch as he jumps up in a mix of excitement and agitation. "Elvis. No! The Beatles! No! Wait. Um." He hits his head to get it working faster, unsurprisingly not doing much to help. "Ugh... that remix. I don't know! I am a bit busy."

"Right, then.