Fiction

Doctor Who: The Sontaran Games by Jacqueline Rayner
Chapters 7–16 [the end]

Well, I can't say the twist truly surprised me, but it is a pretty dark novel, especially by the standards of this era of Who (when it was being more kid-friendly again). It's partly thanks to how much the Sontarans were treated as humorous by the show — the very fact they're in it leads you to expect a light-ish romp, but instead they're vicious, murderous, and genuinely threatening. As one of the series' most-recurring villains, it's only appropriate, really.