Hayder gives us multiple third-person limited narrative focuses for Poppet. The narrative is handled deftly (though Boy, are some of the chapters short!), with Caffery and mental-institution worker AJ being the main protagonists. AJ calls Caffery in when events at his privately funded institution seem to get dangerously weird. And they are dangerously weird, and have been intermittently for years.
Poppet does a number of things tremendously well. Foremost is its sensitive treatment of catastrophic mental-health issues both through the sympathetic, haunted AJ's interactions with his patients, and partially through Poppet's plot, which does not go where it seems to be going. Hayder should get some sort of prize for not giving us the same old mentally ill boogeymen and women, or for ot simply dressing up yet another impossible Joker and unleashing him on her novel.
Terrible things do happen, and marvelous things, some of the latter verging on the supernatural without necessarily getting there. Throughout it all, Caffery -- isolated, alcoholic, workaholic -- holds himself together as he also strives to follow the labyrinthine thread to the truth. Highly recommended.