The man who broke into the Institute, killed your servants, took your Pyxis, and plans to build an army of clockwork monsters to destroy us all – in short, a man who must be stopped.”
-- Consul Wayland (chapter 1)

Importance: Consul Wayland is talking to Charlotte about her assigned task of finding Mortmain. She believes it is impossible, especially on her own, but Consul Wayland is pointing out that Charlotte should be eager to find Mortmain. He says that she might want to reconsider her role as head of the Institute, if she is not ready to embrace this task.

You opened a Pyxis and released a demon. It cursed you. You want me to find that demon and see if it will remove the curse.”
-- Magnus (chapter 2)

Importance: Magnus is talking to Will, and this is the first hint of Will's secret.

Did she really belong to a race of creatures that was at war with what Jem...
-- Narrator (chapter 5)