Gloucester has been murdered. Richard banishes both Mowbray and Bolingbroke and refuses to listen to any good advice. He's run through all the money his ancestors collected, so when John of Gaunt dies, he decides to seize his property to help pay for the war in Ireland.
While Richard goes to Ireland to fight the war, Bolingbroke comes back from his banishment to demand his inheritance. Pretty much everybody thinks he's been treated badly and that Richard is doing a bad job as king. By the time Richard returns to England, he's more or less lost control of the kingdom.
Henry makes Richard publicly give up the crown so that it looks like Richard voluntarily stepped down. (No one really buys this, but it's good for appearances.) Richard is separated from the queen, imprisoned, and eventually killed. Henry executes some enemies, pardons others (like Aumerle), and feels bad about Richard's death. He decides to deal with his guilt by going on a pilgrimage.