The Kindly Ones (The Sandman, #9)

Distraught by the kidnapping and presumed death of her son, and believing Morpheus to be responsible, Lyta Hall calls the ancient wrath of the Furies down upon him. A former superheroine blames Morpheus for the death of her child and summons an ancient curse of vengeance against the Lord of Dream. The "kindly ones" enter his realm and force a sacrifice that will change the Dreaming forever.