The Sword of Summer by Rick Riordan

Magnus Chase has seen his share of trouble. Ever since that terrible night two years ago when his mother told him to run, he has lived alone on the streets of Boston, surviving by his wits, staying one step ahead of the police and the truant officers.

One day, Magnus learns that someone else is trying to track him down—his uncle Randolph, a man his mother had always warned him about. When Magnus tries to outmaneuver his uncle, he falls right into his clutches. Randolph starts rambling about Norse history and Magnus's birthright: a weapon that has been lost for thousands of years.

The more Randolph talks, the more puzzle pieces fall into place. Stories about the gods of Asgard, wolves, and Doomsday bubble up from Magnus's memory. But he doesn't have time to consider it all before a fire giant attacks the city, forcing him to choose between his own safety and the lives of hundreds of innocents. . . .

Sometimes, the only way to start a new life is to die.