Target: The Sea Devils.

I never saw a copy of this as a kid, and I only found one for myself a couple of years ago, it was something like the 135th one I acquired. This rarity is surprising as it was reprinted at least twice. It's a Malcolm Hulke adaptation, which usually means back-story, sarcastic narration about characters' thoughts and long digressions.

In fact not so much character back-story in this, certainly not to the extent that it occurs in The Cave Monsters. There's a page or more about the Master's trial, though, and the special pleas the Doctor put in on the Master's behalf. (Thus increasing the unspoken identification between the two Time Lords, both serving sentences).

There's quite a long digression when the Doctor and Jo arrive on the island, about sunken villages and how the Doctor never met Henry VIII (contradiction there of what the First Doctor says in the story of the parson's nose). Although it's quite atmospheric, it doesn't seem really to work, it feels superfluous, like the bit Hulke sticks on the end of Dinosaur Invasion.

Plenty of Trenchard's thoughts: and unlike on screen, he doesn't get to make a heroic last stand, because the silly old sod forgets to turn off the safety-catch on his revolver, so when he tries to shoot a Sea Devil, nothing happens. (The Doctor, when he sees what's happened, turns the catch off, so people will think Trenchard died heroically. A bit like the white lie he tells about Skinsale in the Fang Rock novelisation).

Think I mentioned this last time, but the prison officers are - instead of slightly romantic, bushy-moustached cloak-wearing types - standard literary/dramatic prison officers from the pages of Borstal Boy or an ep of Porridge. When the Doctor takes the piss out of their 'Am receiving two from you' talk, they even give him the old 'three kinds of people' routine (I actually have heard that from a genuine P.O.).

Various naval petty officers are given names and personalities, a policeman is introduced who comes asking Captain Hart questions, and Walker is much as seen on screen except that he produces a tin of sweets from his pocket when they're locked up in the radio room. (Jo pointedly asks why he doesn't share them, and he says they're made specially for his taste and that she wouldn't like them).

And when the Sea Devils first emerge from the sea and start chasing the Doctor and Jo, the Master rather rudely shouts 'Exterminate them, you ugly idiot'.