That Old Black Magic (War Mages, #1)

Head Auror Harry Potter and his magical partner, Lord Draco Malfoy, are cast back in time against their will and at the whim of fate to right the injustices done during the second blood war. Faced with a nightmare filled future, a looming war, and the forced to deal with people long dead to them–they must navigate the past, protect the future, and learn to forgive before it’s too late.