"42" is the seventh episode of the third series of British science fiction television series Doctor Who. It was first broadcast on BBC One on 19 May 2007. It was the first episode written by future showrunner Chris Chibnall.

A spaceship hurtles out of control towards an alien star and the Doctor has 42 minutes to save the ship, but as the star possesses and murders the ship's crew, the Doctor and Martha are running out of time.

According to the BARB figures this episode was seen by 7.41 million viewers and was the third most popular non-soap-opera broadcast on British television in that week.

The Doctor and Martha receive a distress signal from the S.S. Pentallian, a human spacecraft that is hurtling towards the star of the Torajii system. The Doctor pilots the TARDIS towards it to help, but after arriving they are separated from the TARDIS by the rising temperatures on the ship. The ship's engines have failed and they have only 42 minutes left before the ship plunges into the star. They need to reach the bridge controls but find themselves separated from them by thirty deadlocked doors that are each password encoded. Martha teams with Riley to work their way through the doors, having to answer pop quiz questions in order to open each door. The Doctor helps the engineering team try to repair the engines. Martha uses her modified mobile phone to call her mother Francine on present-day Earth to answer one of the questions. Francine asks questions about the Doctor that Martha ignores.

One of the crew, Captain McDonnell's husband, Korwin, has been infected with something that is causing his body temperature to rise to incredible levels. They attempt to sedate him while they continue the repairs, but the sedative doesn't work and Korwin escapes. He dons a welding helmet and starts killing crew members before infecting a man named Ashton. As Martha and Riley continue to work through the doors, they encounter Ashton and take shelter in a nearby escape pod. Ashton is able to launch the pod despite Riley's attempts to stop him. As the pod falls towards the star, Martha calls her mother and apologises but hangs up when Francine again asks Martha for more information on the Doctor. The Doctor learns of Martha's situation and puts on a spacesuit before going outside the ship and activating a magnetic control that recovers the pod. As the Doctor returns to the spacecraft, he looks at the sun and finds himself infected. He learns that the star is actually a living being and that the crew drew the star's heart to use as fuel despite it being illegal to do so, and now the star is trying to recover its lost parts. Martha puts the Doctor into a stasis chamber to prevent him from regenerating, but Korwin appears and disables the chamber. The Doctor insists that Martha leave him and warns the crew to dump the fuel, which should allow them to escape.

...
Wikipedia