"Wraith World", written by Big Finish veterans Cavan Scott and Mark Wright, hits the ground running, opening with a dramatic flash-forward to the full throes of its alien menace.
That menace is particularly inventive - and gruesome - in its conception. It comprises (not comprised of, as Mr Smith puts it - the supercomputer really ought to have better grammar) hideous, blood-red worms, which engulf Luke and Clyde during one particularly revolting sequence, and combine to form a larger, humanoid creature. The voice of this being sounds not unlike the Ice Warriors, as performed by the vocally treated Elisabeth Sladen.
The notion of fiction becoming reality is less original. The subject has, for example, been explored in Doctor Who - The Mind Robber  [DVD], a story I was particularly reminded of when Sarah Jane, like the Second Doctor before her, engages in a true war of words against another writer towards the end of the adventure.
All in all, though, the fiction of "Wraith World" becomes the reality of spirited adventure and enjoyable escapism.