Just finished it. Yes this is a spin off series from the main Laundry files (we are promised a new entry later this year) this series is set in the same world, different cast of characters where CASE NIGHTMARE has come to pass and the Laundry considered the only way for survival of humanity was to adopt an Elder God and habituate him to society, so that he would want to protect something.
You have superheroes (and villains) rubbing shoulders with mystery cultists, mad scientists, sorcerers, elves, vampires and meat printer mechanics. Charlie’s Near future Supermarket under the New Management is an absolute thing of terror and horror Jim has never managed with the Dresden Files. His Muppets are much much worse than Renfield’s and the vanilla Mr Hewitt far far more terrifying than Mavra.
Also his T-Rex is offed by a Nanny dressed like Missy from Doctor Who. Sue wouldn’t have stood a chance against Mary.
The original series took the works of Le Carre, Deighton and Fleming classic spy fiction as a jump off point into urban fantasy with this series doing the same with classic children’s fantasy, the first book Peter Pan and the second Mary Poppins, so I would expect the Chronicles of Narnia, The Borrowers etc to appear as jump off points for story lines for future books.