Monarchy can be such a drag. King Henry, who's feeling guilty about deposing and then murdering King Richard II, wants to make up with God by leading a crusade. Too bad border wars with Wales and Scotland have put the kibosh on Henry's plans. To make matters worse, an up-and-coming nobleman, young Henry Percy (Hotspur) is trying to front with the king. He refuses to give Henry his valuable Scottish war prisoners unless Henry agrees to ransom Mortimer from the Welsh leader (Glendower) who took him captive. To make matters even worse, King Henry's son, Prince Hal, is acting line a total degenerate, hanging out with common thieves and making the royal family look bad. What's going to happen when this degenerate kid gets his hands on the crown?
The Percys are fed up with the king dissing them and they organize a rebellion (with the Scottish Douglas, the Welsh Glendower, and Mortimer). They say Henry's an illegitimate king – Mortimer should be the monarch because King Richard II said so before he was murdered. Meanwhile, Prince Hal is running amok with his disreputable Eastcheap friends. Hal's wild antics, which include his participation in the robbery of the king's exchequer (treasury) on the road at Gads Hill, seem to be as big a threat to the kingdom as the Percy family uprising. There's just one thing. Prince Hal confides in the audience that he's merely pretending to be rebellious in order to stage a dramatic "reformation" that will make him seem like a glorious leader. Soon after, he tells his dad not to trip – Hal will kill Hotspur in battle, redeeming his honor and saving dad's crown in one fell swoop. Can he pull it off?
Prince Hal makes good on his promise and becomes a war hero during the battle at Shrewsbury. Not only does he save his father's life from certain death at the hands of Douglas, he also kills Hotspur in battle, taking all of Hotspur's "proud titles" and making them his own. Hal has redeemed himself in his father's eyes and the battle has been won. The prince even seems to be pulling away from his bad influence pal, Falstaff. But, there are more rebels to deal with in Northumberland and Wales, so the troops gear up for more fighting. The story continues in Henry IV Part 2.