This feedback was excellent, especially as this is my first query letter. Thank you so much! I did find the final paragraph about the "stakes" especially tricky. I've done a revision - would love it if you could take a look? :)

Dear [AGENT NAME],

As an Aethrian, Lina can step into the aetherial realm, a place of spirits and demons, to help the dead move on. Unfortunately, Lina’s people are held accountable for the actions of one man, Azarias, who flooded the material world with some of those demons sixteen years ago.

Thanks to Azarias, Lina and her people are outcasts. Shunned, feared, even hated. Lina considers herself lucky to be able to live a normal life with her adoptive father, Cephas.

Until she witnesses a brutal murder down a backstreet.

Cephas promises to help Lina deal with what she’s seen, but he doesn’t get the chance. Death snatches him away.

Plagued by death and her growing abilities, Lina is taken in by Cephas’s close friend, Casimir, who promises help in the formed of banned books on Aethrian lore.

Plunged into Casimir’s extravagant life, Lina realizes that dark secrets lurk beneath the riches of the inner city. Casimir has plans of his own for Lina’s powers, and he’s not afraid to blackmail her to get what he wants. With innocent lives hanging in the balance, Lina must embark on a quest that she knows will end in catastrophe. Can she turn things around before it’s too late, or will she ensure that her entire race is executed this time?

REALM OF RUIN is a YA fantasy complete at 72,000 words. I’m currently studying for a degree in English Literature and Creative Writing.

Thank you for your time and consideration.

Sincerely, [name & contact information]