Slow Decay

Slow Decay by Andy Lane concerns a mysterious new weight loss clinic ran by a Doctor Scotus, whose methods work almost instantaneously but whose side-effects are quite (prepare to deploy pun: 3, 2, 1:) monstrous. This was one of the first Torchwood books released, so all the characters are present but Gwen and Rhys' relationship is central to the book's plot and Lane does a great job describing some of the challenges, difficulties, and anxieties couples in their early thirties can face. The novel is paced well, and the combat scenes are suitably gory. There's also an interesting explanation for why Owen became a doctor (in order to keep himself from dying from the same disease that killed his father), an intriguing description of the Torchwood archives, a mysterious reference to an Operation: Goldenrod, and some really nice, dark humor (usually involving Jack ribbing Owen) like the scene where the group has had to capture and bind a monster-possessed girl:

"I hope we're not stopped by the police on the way back to the Hub," Ianto said. "Explaining why we've got a young girl tied up in the back could be tricky."
Jack smiled. "We'll let Owen talk us out of it. I'm sure he's had lots of practice."

Another solid entry in the Torchwood novel line, which, now that I've read eight books, I continue to be impressed by--it's far above Buffy and what I remember of Star Trek novels, and right up there with Star Wars (though the lack of internal continuity is unfortunate).