The Doctor and Martha find themselves trapped aboard a ship that will, in 42 minutes, collide with a sun. Unable to access the TARDIS, there is only one solution: repair the engines that have been sabotaged by Hal Korwin, who has been taken over by an alien being. As the crew races to keep from burning up in the sun, Korwin is killing the crew, one by one. Meanwhile, Martha and another crewman work their way through a series of doors to get to the auxiliary engine controls but soon find themselves trapped in an escape pod which is then jettisoned from the main aircraft. Back on Earth, Martha's mother is still worried about her daughter being with the Doctor and decides to do something about it.
—garykmcd