Ep 3. Air Lock (3)

The Doctor has returned to The Futurekind encampment on the planet Malcassairo, where he and Martha are being held prisoner by the cannibalistic creatures. As the Futurekind prepare to breach the air lock and kill the Doctor and Martha, they are rescued by a mysterious figure in a spacesuit known only as "The Professor". The Professor takes them aboard his ship and informs them that he has been searching for a way to escape the planet for centuries.

The Doctor, Martha, and The Professor are soon pursued by the Futurekind, who manage to board the ship. The trio retreat to a hidden chamber and discover that The Professor is actually a future version of one of the Doctor's old enemies - The Master. The Master reveals that he has engineered a scheme that will allow him to escape the planet and take control of the universe, but he needs the Doctor's help to complete it.

Despite the Doctor's reluctance, he agrees to help The Master complete his scheme, but only if he can ensure that no harm comes to Martha. As they work together, the Doctor begins to suspect that The Master has ulterior motives and is using him for his own ends.

As they near the completion of their plan, the Doctor and Martha are forced to confront The Master's true intentions. The Master reveals that he plans to sacrifice them both in order to achieve his goal of galactic domination. The Doctor is able to outsmart The Master, however, and manages to escape along with Martha.

Back aboard the TARDIS, the Doctor reflects on the dangerous game he played with The Master and the risks he took to save Martha's life. Despite his anger at The Master's deception, the Doctor is left with a sense of unease about the true nature of his own role in the universe.