Guards Bernardo, Horatio, and Marcellus encounter the ghost of the dead King Hamlet on the battlements, learn of looming conflict with Norway and decide to inform Prince Hamlet.
Claudius consolidates power by marrying Gertrude, sending envoys to Norway about Fortinbras, and granting Laertes permission to return to France; Polonius supports this. Hamlet expresses deep grief and disgust over his mother’s swift remarriage, delivers his “O, that this too too solid flesh would melt” soliloquy, and, after hearing the guards’ report of the ghost, vows to join them on watch and confront the apparition.
Laertes cautions Ophelia against Hamlet’s fleeting affection and urges her to preserve her virtue; Polonius delivers a lengthy set of paternal maxims to Laertes, including “to thine own self be true,” and then confronts Ophelia about Hamlet’s advances, warning her that his vows are unreliable and commanding her to cease all contact with him.
The ghost of the dead King appears to Prince Hamlet on the platform; Hamlet confronts and vows to follow it despite Horatio and Marcellus' warnings; Marcellus declares that “something is rotten in the state of Denmark.”
Polonius sends Reynaldo to Paris to discreetly probe Laertes' conduct, and later, after Ophelia reports Hamlet's bizarre and frantic behavior, Polonius decides to inform the king about Hamlet's apparent madness caused by love.
Claudius commissions Rosencrantz and Guildenstern to spy on Hamlet; Polonius attributes Hamlet’s madness to Ophelia’s love and plots to trap him by arranging a meeting behind an arras; ambassadors Voltimand and Cornelius report that Norway’s threat has been pacified and a payment secured; Hamlet exchanges sharp wit with Polonius, delivers the “What a piece of work is a man” soliloquy, confronts Rosencrantz and Guildenstern about their motives, and decides to have a troupe perform a play that will reveal Claudius’s guilt; the Players arrive in Elsinore.
Hamlet delivers the “To be, or not to be” soliloquy, confronts Ophelia and urges her to a nunnery, while Claudius arranges a covert observation of Hamlet’s encounter with Ophelia and resolves to exile Hamlet to England; Polonius and Claudius continue plotting to discover the cause of Hamlet’s apparent madness.
Hamlet gives the Players a detailed instruction on naturalistic acting, denounces over‑acting, and designates the upcoming performance as the “Mousetrap” to trap King Claudius’s conscience.
Claudius orders Rosencrantz and Guildenstern to escort Hamlet to England and Polonius prepares to eavesdrop behind the arras; Claudius delivers a guilt‑filled soliloquy; Hamlet decides not to kill a praying Claudius, postponing his revenge; Claudius muses on the inadequacy of his prayers before exiting.