I struggle a bit with the eight parters. The story is often far too thinly spread out and the plot advances at a glacial pace until it's all wrapped up in episodes seven and eight. This one is slightly different, though, as it neatly separates into two semi-stories. The first sees the "Doctor" (John Pertwee) and "Liz" (Caroline John) drafted in by the "Brigadier" (Nicholas Courtney) to investigate some power outages at a top secret energy installation being run by "Quinn" (Fulton Mackay). Their arrival sets the cat amongst the pigeons, especially with the secretive Scotsman and his assistant "Miss Dawson" (Thomasine Heiner) who seem to know a great deal more about the nearby caves than either are prepared to let on. As the staff start to suffer too, it falls to team Time Lord to investigate and that's when he discovers that there is an ancient Earthly species awakening to find mankind's latter day occupation of the planet a nuisance to their plans. What now? Diplomacy or brute force? The eponymous sleepy-heads are visually akin to the "Sea Monsters" and the story from Malcolm Hulke does adequately, if rather verbally, as it builds up - but there's no work for the TARDIS here and by half way through I felt this wasn't really a "Dr. Who" at all, but a half-decent sci-fi adventure that relied on the usual television studio for most of it's action settings. Is there also supposed to be a moral here? Shoot first, collaborate later? It's all perfectly watchable, and little "Nellie" gets a welcome engine clean, but it takes too long to get going and when it does it becomes a shade predictable. Not one of the better series, methinks.