Dudley also wrote novelisations of his two other two-episode Who stories. Doctor Who - Black Orchid is possibly the best Fifth Doctor novelisation; Doctor Who - The King's Demons is one of the worst. Of the three stories as televised, Black Orchid was OK, K9 and Company dull and The King's Demons pretty dire, so I was curious to see how Dudley would manage turning this one into print.
It's not too bad, in fact. The beginning is a bit ropey, with Dudley insisting on giving us the exact age of each character, and some dubious descriptions of Sarah's problems in an Ethiopian village; but it settles down and has a lot more oomph than the original. Sarah is explicitly a "girl" (as compared to Elisabeth Sladen's svelte but mature 33 when this was made). She is tough; she sometimes prays; she has a black belt in karate; she loves driving her MGB (and there is a great chase sequence absent from the original TV version).
Some other things done to continuity: Aunt Lavinia has become an anthropologist rather than a virologist, which gives her an excuse for writing to the newspapers about witchcraft; Brendan is explicitly 14, so the reference to him doing three extra O-levels has been dropped. (As indeed O-levels had been by 1987.) The red herrings of the original (Aunt Lavinia's mysterious disappearance, the not-so-sinister Bakers) are retained without further explanation. For some reason K9 sings "While Shepherds Watched" rather than "We Wish You a Merry Christmas" at the end.
So, more towards the Doctor Who - Black Orchid than the Doctor Who - The King's Demons end of the spectrum, and without the silly mistakes that marred the former.
I decided to re-watch the original TV story after reading the book. My memories from two-thirds of my lifetime ago were right: it is indeed not bad but not actively interesting. Ian Sears as Brendan is a particularly weak point - an unispired performance and doesn't change out of school uniform until halfway through (just before he is kidnapped). Worse, he is the first in a line of crap young male sidekicks inflicted on Sarah Jane in the spinoffs. (Jeremy Fitzoliver in the two Third Doctor audios, Josh Townsend in her Big Finish series - though at least the latter turned out to have hidden depths). Well done RTD and colleagues for shifting to the more successful formula of the Sarah Jane Adventures. Of the other cast, veterans Bill Fraser and especially Colin Jeavons are rather delightful. The excellent car chase from the book is a single close encounter with a tractor. Really one for completists only.