Richard II is the first of three plays (the others are Henry IV Parts 1 and 2 and Henry V) called a tetralogy or, as some others say, a Henriad.
The story opens with the King trying to adjudicate a quarrel between Bolingbroke and Mowbray. This escalates to a duel, but as that begins, Richard sends both into exile and thereby his troubles begin in earnest. In trying to wage monies for a war with Ireland, he enrages not only the nobles but the commoners too. When John of Gaunt, Bolingbrook’s father, dies and his land and monies are seized by Richard, Bolingbroke is encouraged to return. He does and so sets the stage for the overthrow of Richard and his own ascension as King Henry IV (Henry IV is also available in this series).