Ep 7. The Ark in Space (3)

The Doctor and her companions are back on the TARDIS, but something seems off. The Time Lord is acting slightly different, and there's a sense of urgency in her behavior that her travel mates can't ignore. They find out that she's received a distress signal from an ark in space - a vast space vessel carrying the last of humanity in cryogenic sleep. The ship was launched from Earth to escape a solar flare that would have destroyed all life on the planet.

The TARDIS materializes on the ark, which has been drifting aimlessly in space for centuries. The Doctor discovers that a sentient alien race called the Wirrn have infiltrated the ark and are using the stored human DNA to turn the inhabitants into hosts for their larvae. The Wirrn are a hive mind, and their plan is to find a new planet to colonize and continue their species.

The Doctor and her companions work with the few human survivors they find and devise a plan to stop the Wirrn, but they face incredible difficulties. The Wirrn are fast, agile, and seem to have an instinctive understanding of their hosts' behavior. Moreover, they're already inside the ark's life support systems, and can adapt to any situation they encounter. The Doctor realizes that the only way to stop them is to destroy their breeding chambers, but to do that, she needs to venture outside the ship - a dangerous and risky proposition.

As the team struggles to find a way to access the breeding compartments, the Wirrn launch wave after wave of attacks. The Doctor faces them head on, never losing her cool or her ingenuity. Her companions, too, rise to the occasion, aiding in the strategic planning and carrying out daring rescues.

Eventually, they succeed in their mission, at great cost. The survivors look up to the Doctor with gratitude and appreciation, knowing that without her, they would have been doomed. The Time Lord, too, is reflective and solemn, acknowledging the fragility of human life and the importance of protecting it.

The episode is fast-paced and suspenseful, and the acting is uniformly strong. The interactions between the Doctor and her companions are heartfelt and genuine, and the characters feel fleshed out and well-rounded. The set and creature design is also impressive, creating a sense of claustrophobia and tension that persists throughout the episode.

Overall, The Ark in Space (3) is an exciting and thought-provoking installment of the Doctor Who series, showcasing the intelligence, bravery, and compassion that make the Doctor such an enduring figure. It stands as a testament to the power of teamwork and unity in the face of overwhelming odds, and is sure to leave viewers satisfied and contemplative.