Thor is the teenage prince of Asgard, son of Odin, chafing under a sheltered life and hungry to prove himself a true warrior. Undefeated in the training arena, he is stung when Sif tells him the celebrated Einherjar let him win because no one dares defeat the king's son, and Odin confirms it. Denied permission to ride out and test his mettle, he defies his father and sets off in secret on a forbidden quest for the legendary Sword of Surtur, said to lie hidden in the frozen wastes of Jotunheim, stowing away aboard the Warriors Three's vessel with his younger brother Loki in tow.
His recklessness carries a heavy price. He finds the sword, but in the escape he slays two Frost Giant sentries, an act that shatters Asgard's fragile truce and brings King Thrym's armies to war. When his father's trusted advisor Algrim, a survivor of the Dark Elves, betrays them and turns the fire sword against Odin, Thor watches his father fall gravely wounded. With Algrim defeated, rather than let the killing go on, he humbles himself, returning Elder Steel to the Frost Giants and offering his own life as prisoner to end the conflict. Thrym spares him, the war ends, and Thor comes away having learned the hard cost of pride and the true value of peace, at last seen by his father as a man rather than a boy.
