Another Evil Grandfather

Hogwarts discovers that Voldemort's daughter (who gave up using magic years ago) has a very powerful son. His name is Percy Jackson. They decide that they will teach Percy magic while keeping an eye on him. Harry is almost positive that he's hiding something but can't figure out what it is. Then to make things even more complicated, Voldemort is rising and this time he has help.

this takes place after BoO and the deathly hallows. in this all the seven have died except for Percy and Annabeth and while they were in Tartarus they were captured by the giants and tortured. Percy blames himself for the senen's death and both of them have so much ptsd from everything that they can't sleep apart from each other.