In the wake of the tragic death of Livia Blackthorn, the Clave teeters on the brink of civil war. One fragment of the Blackthorn family flees to LA, seeking to discover the source of the disease that is destroying the race of warlocks. Meanwhile, Julian and Emma take desperate measures to put their forbidden love aside and undertake a perilous mission to Faerie to retrieve the Black Volume of the Dead. Dark secrets and forbidden love threaten the very survival of the Shadowhunters.