One young woman realizes how dark the city can really be when she learns the truth about her past.

With the knowledge that Valentine is alive and on the hunt for The Mortal Cup, the Institute is on high alert. Not wasting any time, Jace jumps into action and figures Clary’s memories are the key to finding Jocelyn and The Mortal Cup. Unfortunately, Clary’s memories were wiped leaving her without any recollection of this other life that could help her and the team. With only one other option remaining, Jace, Isabelle and a very reluctant Alec take Clary to the City of Bones to face the powerful Silent Brothers.

Meanwhile, Luke continues his search for Clary, and Simon tries to come to terms with his best friend’s new life.

After getting a clue about who may have wiped Clary's memories, the crew hunts down the High Warlock of Brooklyn, Magnus Bane. With all of the warlocks in hiding from Valentine, the team must lure Magnus out with something he can't refuse - a killer party and something very valuable. But with emotions running high, more may come out of their meeting with Magnus than just the retrieval of Clary's memories.

Meanwhile, Simon doesn't seem to be himself after his recent Downworlder encounter.

After piecing together the clues as to where her mother hid the Mortal Cup, Clary, Jace, Alec and Isabelle are on the clock to find its hiding place before anyone else. But with demons and Downworlders lurking everywhere, obtaining the Cup may not be as easy as they had hoped.

Meanwhile, as Simon's symptoms become increasingly worse, he fears he is turning into a vampire.

After receiving important intel about Valentine from a surprising ally, Clary, Jace and Luke devise a plan to rescue Jocelyn. With the mission looking almost impossible, the three will stop at nothing to rescue Clary’s mother and put a stop to Valentine once and for all.

Meanwhile, Inquisitor Herondale arrives at the Institute for Isabelle’s trial as Alec turns to Magnus for help.