Kraken

Billy Harrow curates the Darwin Centre at London's Natural History Museum, and his prize exhibit is a preserved giant squid. When the entire specimen, tank and all, disappears without a trace, Billy is pulled into a hidden London where magic is real and everyone is waiting for the end. A cult called the Church of God Kraken worships the missing squid as a deity. A pair of terrifying enforcers named Goss and Subby hunt Billy through the city. Rival prophets, unionized familiars, and warring sects all read the theft as a sign that their particular apocalypse is finally at hand. Billy has to work out who took the squid and why, before one of the competing doomsdays actually arrives.