The Sarah Jane Adventures: The Eternity Trap

Professor Celeste Rivers (Floella Benjamin) of the Pharos Institute, last seen in The Lost Boy and Day Of The Clown, is conducting a scientific investigation in the supposed existence of the supernatural in an old stately home, where an evil 17th Century alchemist called Erasmus Darkening was said to have practiced his magical craft.

Skeptical Sarah Jane has been invited along to report on the investigation and Rani and Clyde have tagged along (there's no real explanation for Luke's absence, beyond his total disinterest in ghost stories).

No sooner are Sarah Jane and her companions settled in the house, with Professor Rivers and her strangely excitable young assistant Toby Silverman (Adam Gillen), than strange things start happening - faces are glimpsed in mirrors and on video monitor screens, unexplained noises are heard, object float in the air and a book opens on its own to a picture of Darkening.

Then the professor disappears from the nursery and when the others go to find her all the toys start moving on their own and the words "get out" appear on a chalk board.

Splitting up to investigate, Sarah Jane receives a warning from a pair of ghostly children, is attacked by a mysterious creature and saved by a cavalier while Clyde and Rani discover Darkening's laboratory and the man himself (Donald Sumpter)... very much alive after hundreds of years!

And while Darkening is - unsurprisingly - revealed to be a stranded alien, using humans to fuel his faulty trans-dimensional accelerator in an effort to return home, it doesn't stop The Eternity Trap from being wonderfully spooky.

As in any good 'ghost' story, ultimately a lot is left to the viewers' imagination (such as the nature of red-eyed beast haunting the grounds and even the final fate of the many people Darkening had trapped inside the house), but perhaps it was slightly too open-ended. As Sarah Jane - and thus the programme - was trying to explain to a young audience that ghosts are simply figments of overactive imaginations, perhaps a bit more time could have been spent clearing up the smaller details.

I also felt that dismissing Darkening as just "an alien", without any further details or specific reference to his species or homeworld, was a bit of a cop-out; but I expect Phil Ford didn't want to overload his script with proper names and technobabble.

After the incredible five-star first episode of the story, the second had a lot to explain away and deal with and some little nuggets probably slipped down the back of the sofa during the rush to tie everything up in 28 minutes.

Nevertheless, The Eternity Trap was a very creepy story that was simply dripping with great atmosphere, while treading the fine line between a full-on children's ghost story (it made me think of Tom's Midnight Garden, for instance) and a science-led investigation to give logical, rational explanations for supernatural phenomena (The Stone Tape got a namecheck; this BBC play was, of course, written by Nigel Kneale, the creator of Quatermass, the 'spiritual forefather of Doctor Who').

Next Week: Mona Lisa's Revenge