Once again, the TARDIS shows it has a mind of it's own as the "Doctor" (Tom Baker) finds himself stuck with his new pal "Harry" (Ian Marter) and "Sarah Jane" (Elisabeth Sladen) on a spaceship full of folks in cryogenic stasis. Something isn't right though, not least because she has had to be put in one of the pods and there are the remnants of a rather large insect in the cupboard. They release "Vira" (Wendy Williams) and the mission commander "Noah" (Kenton Moore) from their slumbers and are soon on the wrong end of the menacing "Wirrn" who are looking for juicy hosts for their offspring and seeking revenge for humanity's unkindness on their own home-world centuries past. The "Doctor" et al now have to find a way to stop them from turning into an invincible swarm. This is one of the better stories, well written and focused into four episodes. Marter is now an useful member of the team and the triumvirate is working well at keeping the pace of their adventures tight and entertaining. This one also features some better than average latex-work and a slightly more cerebral plot that might interest the entomologists amongst us.