Harry and Sirius reunited in Harry's fifth year at the leaky cauldron after Harry and his cousin Dudley were attacked by dementors. Harry went on with his fifth year at Hogwarts, but, still having dreams about Voldermort, and pains in his scar. When Harry and the Weasleys arrived at Grimmauld Place just after Arthur was attacked by Nagini, Sirius was unshaven and still in his day clothes late at night. He also seemed to have taken to drinking, as he had a "Mundungus-like whiff of stale drink about him". However, Sirius made a complete turn-around when the Weasley family and Harry decided to stay at Grimmauld Place over the Christmas holidays for its proximity to St Mungo's, and at one point was heard singing "God Rest Ye, Merry Hippogriffs" at the top of his lungs. Voldemort used Legilimency to implant a false vision into Harry's mind that Sirius was being tortured in the Department of Mysteries, convincing Harry that Sirius had in fact been captured. After giving Severus Snape a cryptic message informing him of the situation and then ditching Umbridge in the Forbidden Forest, Harry, along with Ron, Hermione and fellow D.A. members Ginny Weasley, Neville Longbottom, and Luna Lovegood, flew to London via Thestral. The students made their way through the deserted Ministry of Magic and gained access to the Department of Mysteries, only to be ambushed by Death Eaters. It was Snape who ultimately saved their lives by alerting the Order to what Harry had seen; Sirius, Kingsley Shacklebolt, Nymphadora Tonks, Remus Lupin, Alastor Moody, and eventually Albus Dumbledore, arrived at the Ministry and began battling the Death Eaters.
Tragically, however, during a frenzied duel with his hated cousin Bellatrix, Sirius was struck with an unknown spell causing him to fall through the Veil in the Death Chamber to his death. It would be years before Harry could fully come to terms with the loss of his godfather, who, as Dumbledore flatly stated, was the "closest thing to a parent" Harry had ever known. Harry Potter blamed himself for Sirius' death.