The Doctor tries to return to the TARDIS but it has been parked in a vent chamber, and is now inaccessible. Instead he decides he must fix the engines of the ship and runs off to the engine room.
On arrival he finds the engines wrecked, and theorises that they have been sabotaged. As the captain of the ship, McDonnell tries to contact the other members of the crew the Doctor suggests using the auxiliary controls. However other members of the crew point out that they lie behind 29 deadlock-sealed password-protected doors.
The Doctor sends Martha and a crewmember named Riley to unlock the door whilst the others are called to the medical centre.
“Impact in 34:31”
In the med centre crewmember Korwin struggles against two others, Abi and Ashton, as they try to put him in stasis. It is he who sabotaged the ship after succumbing to rising body temperature. The Doctor tells the others to keep his internal temperature regulated and sedated, before rushing back downstairs.
“Impact in 32:50”
At the first door Riley explains to Martha that the passwords are the answers to random questions set by the crew. They pass through the first but get stuck at the second, which requires the answer to a mathematical sequence. The Doctor aids them over the intercom and they move on to the next.
“Impact in 30:50”
Stumped by a question on music they again call the Doctor but he is busy making a back up should Martha and Riley fail to reach the auxiliary engines.
“Impact in 29:46”
Martha calls her mother to get the answer to the question but she is more concerned about the Doctor. As she connects to the Internet the computer sound
“Impact in 28:50”
The Doctor receives a message from Abi, who explains that Korwin’s body is changing. She turns around to find him standing over her and calls for urgent assistance. The Doctor runs to help but as Korwin, whose eyes are closed, advances on her it becomes to late. In a rasping voice he proclaims; “Burn with me!” He opens his eyes to reveal a blinding light within and Abi screams out in pain.
Francine manages to find the correct answer and Martha and Riley progress, Martha having to severe the phone line when Abi’s scream rings out over the intercom. In the med centre Korwin places a helmet over his head and stalks away, leaving the Doctor and McDonnell to find the vaporised remains of Abi. The Time Lord examines Korwin’s medical chart and realises that he has been taken over by an alien force.
McDonnell, Korwin’s husband, becomes distraught but warns the crew that Korwin is dangerous and on the loose. Elsewhere Erina, another crewmember fetches tools for the repair work but is stopped by Korwin, who lifts his visor to expose her to the light.
In the med centre the Doctor is forced to admit that Korwin cannot be saved, but continues to try and find out what force has made its way onto the ship. Martha and Riley continue on their journey as Korwin moves onto his next victim, Ashton. He reaches forward and clasps his head, his bare hands burning his skin.
Soon Ashton advances on Riley and Martha, wearing a helmet like Korwin’s. He calls out to them “Burn With Me” and they flee, making their way to an escape pod. Ashton tries to jettison it but Riley manages to counteract it as Martha tells the Doctor.
Soon McDonnell and Scannell return to the engines, only to find them damaged even further. Korwin arrives and his wife tries to reason with him, only for him to blame her for what has happened.
The Doctor arrives at the escape pod to confront Ashton, who smashes the release circuit locking the jettison programme. Scannell managed to blast Korwin with the ice vents as the Doctor faces Ashton, who appears to feel Korwin’s pain. He stalks away and the Doctor warns Scannell, who claims that Korwin is dead.
The Time Lord then tries to free Martha, only to find it is too late. As they each gaze through a portal at each other the escape pod departs from the ship, toward the sun.
“Impact in 17:05”
Scannell asks McDonnell why Korwin claimed it was her fault, but she avoids the question. He is called to meet the Doctor whilst McDonnell decides to deal with Korwin.
Inside the pod Martha sits in hope of rescue as Riley claims it is too late. Their conversation talks to families, and Martha begins to realise she may never see hers again. Riley tells her to call them.
McDonnell confronts Ashton and manages to place him in a stasis chamber, subjecting him to temperatures of –273 degrees Celsius. Elsewhere, the Doctor dons a spacesuit and prepares to try and recall the escape pod from a control panel on the outside of the ship.
Martha calls her mother again and tells her she loves her. She is unaware that Francine is not alone; a mysterious woman is recording their conversation from the next room. As she asks again if Martha is with the Doctor Martha hangs up, leaving Francine alone with the woman.
“Impact in 11:15”
The Doctor opens and air lock and struggles to step outside. Grabbing hold of the airlock door he reaches over to the control panel, first activating a series of buttons. He then reaches for a rusted hatch covering a lever. With a cry of agony he managed to grab the lever and activate it, pulling the escape pod back toward the ship. However as he steps back inside he looks into the heart of the sun, realising that it is alive.
“Impact in 8:57”
The Doctor stumbles back into the ship and Martha, Riley and McDonnell join him. Riley moves off to help Scannell with the doors as the Doctor opens his eyes, revealing the blinding light that infected Korwin and Ashton. He blames McDonnell for all that has happened, explaining that she mined the sun for cheap fuel. In actuality she mined out the heart of a creature that took the form of a sun, a creature that now lives inside the Doctor. Struggling to regain control he tells Martha to take him to the stasis chamber
“Impact in 7:30”
Back in the engine room Korwin begins to awaken, and Riley and Scannell race to unlock the remaining doors. In the med centre Martha prepares to subject the Doctor to ice cold temperatures, and he finally admits to her that he is scared. She tries to calm him and activates the stasis chamber, causing him to scream out in pain.
Korwin rises from the floor and uses a control panel to close down the power of the stasis chamber. The Doctor writhes in agony as McDonnell rushes to solve the problem.
“Impact in 4:47”
Riley and Scannell continue to hurry and the Doctor orders Martha go to the front of the ship and dump the fuel mined from the sun. She promises to return and runs off.
“Impact in 4:08”
McDonnell manages to find Korwin and she accepts the blame for what has happened but as Korwin advances she is forced to run away, her lost husband following.
“Impact in 3:43”
Martha runs as Korwin continues to track McDonnell, finding her cowering in an airlock. Again she faces him and begs him to stop, before sealing the doors. She apologises to her crew and opens the air lock, she and Korwin plummeting into the sun in a final embrace.
“Impact in 2:17”
Riley and Scannell arrive at the last door as the Doctor escapes from the stasis chamber. Still struggling to suppress the force inside him he crawls along the floor and contacts Martha over the intercom
“Burn with me Martha”
Riley and Scannell open the last door and reach the auxiliary engines, but they appear not to work
“Impact in 1:06 Collision Alert”
Martha arrives, telling them to vent the engines and dump all of the fuel. They do so and as the fuel plummets into the sun the Doctor’s eyes, once filled with light, return to normal. The engines roar to life and the ship begins to fly away from the sun.
Riley and Scannell rejoice as Martha rejoins the Doctor, who is now his normal self.
Some time later the TARDIS is retrieved, Riley and Scannell remaining onboard to await the authorities. As the Doctor steps inside the ship Riley kisses Martha goodbye and she too makes her way inside. She jokes about not really needing the Doctor but his stone-clod expression stops her in her tracks.
She asks how he is coping but instead he avoids the question, instead handing her a copy of the TARDIS key. She suddenly recalls leaving her mother somewhat abruptly and calls her again. She apologises for her past abruptness and agrees to meet her for dinner, making sure of the date: Election Day. Again she hangs up before the subject of the Doctor arises and Francine is left to confront the mysterious woman monitoring her conversations. She hands over her mobile phone and she is thanked for her work.
“Mister Saxon will be very grateful”