james and cordelia are now married. both in love with each other but neither is aware the other reciprocates that feeling etc.
someone is going around murdering shadowhunters. james thinks it might be him because he has nightmares of it every time and there are signs that he's getting out of bed in his sleep.
cordelia's father (still an alcoholic) demands that james give him money. james refuses and sends him away. next day he turns up dead and cordelia blames james for it. she notices his voyance rune is missing, which leads to the discovery that every murdered shadowhunter has had their runes stolen.
cordelia thinks cortana is rejecting her so she goes to wayland the smith who fixes it and makes her swear she will be his paladin.
james ties himself to his bed with cordelia in the room and the rest of his friends around the house. thomas goes on patrol on his own (and alastair secretly follows him) and finds lilian highsmith bleeding to death, which puts him at the murder scene and he gets accused of killing her.
they lock thomas up in the sanctuary waiting for the mortal sword to arrive to be questioned. alastair gets locked up with him after he admits to following thomas around.
lucie and grace ask malcolm fade for help bringing back jesse (apparently belial put a piece of himself in jesse so he could possess him easily) and malcolm agrees to help them if they bring him news of annabel blackthorn. grace finds out from tatiana that annabel had been dead for a hundred years and her family lied to malcolm and told him she became an iron sister.
the murderer attacks charles but fails to kill him. james and cordelia have a fight with belial who now looks like jesse because he's possessing him. and then lilith shows up and she's like you stupid stupid girl you thought you were gonna be wayland the smith's warrior but it was ME pretending to be him and now every time you raise your blade you will be raising it in my own name (interrupting again to say this is one of the dumbest plot points in all of the shadowhunters books imo)
james shoots lilith with this gun that only he can fire for some reason. then lucie is like nooo don't stab jesse. and she commands jesse to purge belial from his body
when belial is cast out of jesse's body, cordelia stabs him a second time, which leaves them with one more fatal wound to get rid of him entirely.
they find out belial was stealing the runes using a device which basically lets you suck up a rune and then deposit it elsewhere (on jesse's body in this case). belial sends a shape shifting demon to pretend to be matthew and tells christopher to give him the device.
lucie basically commands jesse to come back to life.. and runs away with malcolm because she literally did necromancy and that's a big no no.
james finally realizes that grace had him under a spell when he kisses cordelia and grace's bracelet breaks. grace shows up at his door telling him she loves him and he's like what the fuck did you do to me i'm gonna call the silent brothers on you.
cordelia sees grace hugging james and gets the wrong idea so she runs away to matthew's house. so they're both depressed and wallowing in their problems and they decide to run away to paris.
james almost catches up to them but then will stops him and tells him lucie is missing and they have to find her.