The occupants of the TARDIS are a bit puzzled when it stops but keeps moving at the same time! Maybe they are in something, or on something? Well that's what it turns out to be - they are on a ship that seems to be on auto-pilot with two dead crewmen still at their posts. Except, they are not dead - just in stasis and when they awaken they warn the "Doctor" (William Hartnell) et al to get going before they face the monsters who are terrorising them. Too late. The aforementioned creatures - the "Sensorites", have pinched the lock to their time machine and left them stranded. Thing is, are these creatures really so nasty? They don't ever kill so the "Doctor" and "Barbara" (Jacqueline Hill) decide that trying to communicate might be better good idea - and that leads them to their home planet where the race are slowly dying out and attempts to help are being thwarted by more militaristic elements amongst the administration who want to see the back of these meddling aliens. When "Ian" (William Chesterton) comes down with the same sickness, it's soon a race against time.... This series is far too long, with six episodes taking a meandering route through a story that's a bit thin, very dialogue heavy, and just a bit dull.