This is a pleasantly diverting cosmic-horror romp.
When Diana, looking for an apartment to rent, finds one that almost seems made for her - right down to the posters on the walls - it comes with a catch, an unspeakable monster from Beyond called Vom the Hungerer. Diana is supposed to keep Vom shut up in a cupboard: she can only leave her home if she lets him out, but if she lets him out, he eats her.
Diana's new home isn't the only one housing strange secrets. There is Chuck, who's scared - almost - to death of the apparently sweet puppy that guards his front door. There's the couple who share a Thing between them, taking turns to host it.
Diana has stumbled across one of those places where other worlds leak over, all sanity-blasting horrors and strange angles. It is a place where the future of the Universe(s) is daily at risk and having to be rescued by the ordinary seeming caretaker to the block, assisted, now, by Diana, whose exposure to the uncanny has given her magical powers (as well immortality - so long as she manages to avoid being eaten by Vom).
Add to this a buch of crazed cultists worshiping fenris, a being from another dimension who just wants to get home - except that getting home means eating the Moon and rending the fabric of reality - the real threat that the world will be taken over by giant ants - and the difficulties of Diana having any sort of social life whille accompanies by Vom, Zap, Pogo (the apparently sweet puppy) and a string of other horrors, and this is a cheerfully entertaining take on cosmic horror, reminding me in part of Agent to the Stars
in which John Scalzi takes a similarly irreverant line with UFO visitors. Great fun to read, no need to look for anything profound.