When Laertes receives word of his father's death, he drops everything in Paris, immediately returns to Denmark, organizes a mob, storms the castle, and bursts into the King's chamber like awesome, ready to deliver some serious hardcore retribution to his father's murderer. And then for an encore, he kills the titular character in the very next act.
Hamlet's killing of Claudius in the final scene.
Hamlet: The point!—envenom'd too! Then, venom, to thy work. (Stabs Claudius)
Hamlet's letter describing his MacGyvering an execution order for Rosencrantz and Guildenstern, and his escape from the ship.