City of Lost Souls (The Mortal Instruments #5) by Cassandra Clare

Synopsis What price is too high to pay, even for love? When Jace and Clary meet again, Clary is horrified to discover that the Lilithโ€™s magic has bound Jace together with her evil brother Sebastian, and that Jace has become a servant of evil. The Clave is out to destroy Sebastian, but there is no…