This is a bit of an odd book for me. The first half or thereabouts is pretty fun. The monsters, the Shroud, feed on human grief and have come to Earth on November 23, 1963 to eat everybody saddened by the Kennedy assassination. The Doctor and Clara have to stop this new threat, of course, and they get some assistance from the locals to do so. Clara is written relatively well, and the Eleventh Doctor is great in this - the author captures him perfectly in mannerism and speech. I could really picture this as an actual episode. I loved the references to Doctor Who continuity, from the opening scene at the Tottenham Court Road junkyard to the mentions of past companions and monsters.
However, things really went off the rails in the latter half of the book. The Doctor decides that since he's never met the Shroud before, he should track it back to it's previous feeding grounds. In a nice reference to Planet of the Dead, he does this by driving an ambulance through a wormhole (the TARDIS is out of commission because of course it is). And suddenly we get the Planet of the Winter Clowns. It's as ridiculous as it sounds - having been drained of all grief, the people of the planet the Shroud has devastated have reverted to various primal instincts and emotions, except for a small handful that survived fully intact and have turned to clowning to try to fix the population. I get that the author is going for a joy/laughter versus sadness theme, something which Doctor Who has done well in the past, but clowns is a little too on the nose and a little too ridiculous even for Doctor Who (especially nuWho). Plus, it comes down to the Doctor to actually fix things in the end, and the clowns only help him out some.
There's some cool moments of the Doctor revisiting the deaths of past companions, and the idea of every Doctor visiting the Brigadier's funeral is a much better tribute than the crap we got in the season 8 finale. But, I mean, really: clowns. Freaking clowns. It just doesn't really gel with the vibe of the first half of the novel and takes me out of the tension and drama. The result is that while this book has some fun ideas and some neat references to Who's past (it was published in the 50th anniversary year) it just doesn't really hold together for me. I enjoyed parts of it enough to give it three stars, but I'm left disappointed at the wasted potential. I hope the other Doctor Who novels I have are more like Touched By An Angel and less like this mess.