"I have fought the worst things from the darkest corners of the universe. You don't stand a ghost of a chance!"
IN THIS ONE... The team's final battle with Erasmus Darkening to hopefully free the ghosts.
REVIEW: Though "scientific" revelations fly, they really can't explain the Sapphire&Steel level of spooky shenanigans happening in The Eternity Trap - Rivers talking through a phonograph record and so on - nor does the story answer all the questions it raises to bring it to a satisfying close. Marchwood and his kids are evidently reunited at the end, though still "ghosts", but what happens to the rest of the house's inhabitants who felt they were in "Purgatory"? If their lives were snuffed out, why are the Marchwoods still "alive"? Either way, Sarah Jane's a bit flippant about the whole thing. Either she's just condemned all those people to death or to eternal haunting. And what happened to the growling creature that escaped from the portal/rift created by the house? Did Marchwood finally kill it, was the portal closed with the monster behind it, what?
As an adventure story, it still works fairly well, give or take some lighting issues (some scenes are too dark, which doesn't come off as atmospheric so much as murky). Erasmus Darkening is an effective if two-dimensional villain, brilliant but arrogant. And though the episode threatens to become the ghosts' story, the regular cast manages to retain some agency. Lord Marchwood saves the day once too many times, but it's still Sarah Jane who hatches and ultimately puts into effect the plan to destroy the baddie. The kids need more to do than run away from the ghostly phenomena (especially considering that most of it was created by Marchwood to get them away from danger) and fabricating outrageous puns.
Oddly, it looks like they're trying to start something with the character of Toby, but it's never followed up on. He was visited as a child by a gray entity with no face (could be the Trickster or something else entirely), which has sent him into paranormal studies, in spite of his famous physicist father's objections. That's a lot of unexplored backstory for a one-off character. Maybe there were plans for it, I have no idea. I would have taken that over Professor Rivers returning (which she does, once more). She's one of those comedy adults I find so unbelievable as people.
THEORIES: There is a theory going around that Erasmus was a Time Lord, and referencing the Doctor as an alien that also has a human form, and then the TARDIS which apparently also has a "transdimensional accelerator" might point to some intent, though not confirmation, from writer Phil Ford. Perhaps the impulse to make Donald Sumpter into a Time Lord is too strong to fight. To be fair, his costume isn't unlike what Time Lords routinely wear, and his secret chamber could have been a TARDIS damaged so that the whole house became dimensionally unstable (see TARDIS malfunction episodes in the Moffat era). His obsession with immortality is rather like that of other villainous Time Lords like the Master and Borusa; he may be on his last regeneration. As to why the Doctor doesn't sense him, vibrating at some ghostly dimensional frequency could certainly account for it. Imagine if the Doctor knew Sarah had destroyed one the last remaining members of his species...
REWATCHABILITY: Medium - The review makes it sound worse than it is. It's a fine spooky SF story with a charismatic villain. It just falls short of its potential, is all, and on almost every front.