Torchwood: Slow Decay by Andy Lane.  While the story title, and the introductory subplot involve a strange alien communication device (akin to series 1's 'ghost machine'), the real focus of this tie-in is a sinister weight loss clinic that makes people deadly cannibals. Rhys and Gwen are once again having relationship problems (but when aren't they?) because of Gwen's involvement with Torchwood, and Rhys decides he could do to lose a bit of weight himself.. It's an extremely light and silly pulp entry to what little there is of the Torchwood canon, and it does fit with what I've seen of the series thus far, so I can't complain too much.