The play begins with Richard (called "Gloucester" in the text) standing in "a street," describing the accession to the throne of his brother, King Edward IV of England, eldest son of the late Richard, Duke of York.
- Now is the winter of our discontent
- Made glorious summer by this sun of York;
- And all the clouds that lour'd upon our house
- In the deep bosom of the ocean buried.
("sun of York" is a punning reference to the badge of the "blazing sun," which Edward IV adopted, and "son of York", i.e. the son of the Duke of York.)
Richard is an ugly hunchback who is "rudely stamp'd", "deformed, unfinish'd", and cannot "strut before a wanton ambling nymph." He responds to the anguish of his condition with an outcast's credo: "I am determined to prove a villain / And hate the idle pleasures of these days." Richard plots to have his brother Clarence, who stands before him in the line of succession, conducted to the Tower of London over a prophecy he bribed a soothsayer to finagle the suspicious King with; that "G of Edward's heirs the murderer shall be", which the king interprets as referring to George of Clarence (without realizing it actually refers to Gloucester).
Richard now schemes to woo "the Lady Anne" – Anne Neville, widow of the Lancastrian Edward of Westminster, Prince of Wales. He confides to the audience:
"I'll marry Warwick's youngest daughter. What, though I kill'd her husband and her father?"
The scene then changes to reveal Lady Anne accompanying the corpse of the late king Henry VI, along with Trestle and Berkeley, on its way to be interred at St Paul's cathedral. She asks them to set down the "honourable load - if honour may be shrouded in a hearse," and then laments the fate of the house of Lancaster. Richard suddenly appears and demands that the "unmannerd dog" carrying the hearse set it down, at which point a brief verbal wrangling takes place.
Despite initially hating him, Anne is won over by his pleas of love and repentance and agrees to marry him. When she leaves, Richard exults in having won her over despite all he has done to her, and tells the audience that he will discard her once she has served her purpose.
The atmosphere at court is poisonous: The established nobles are at odds with the upwardly mobile relatives of Queen Elizabeth, a hostility fueled by Richard's machinations. Queen Margaret, Henry VI's widow, returns in defiance of her banishment and warns the squabbling nobles about Richard. Queen Margaret curses Richard and the rest who were present. The nobles, all Yorkists, reflexively unite against this last Lancastrian, and the warning falls on deaf ears.
Richard orders two murderers to kill Clarence in the tower. Clarence, meanwhile, relates a dream to his keeper. The dream includes vivid language describing Clarence falling from an imaginary ship as a result of Gloucester, who had fallen from the hatches, striking him. Under the water Clarence sees the skeletons of thousands of men "that fishes gnawed upon." He also sees "wedges of gold, great anchors, heaps of pearl, inestimable stones, unvalued jewels." All of these are "scatterd in the bottom of the sea." Clarence adds that some of the jewels were in the skulls of the dead. He then imagines dying and being tormented by the ghosts of his father-in-law (Warwick, Anne's father) and brother-in-law (Edward, Anne's former husband).
After Clarence falls asleep, Brakenbury, Lieutenant of the Tower of London, enters and observes that between the titles of princes and the low names of commoners there is nothing different but the "outward fame", meaning that they both have "inward toil" whether rich or poor. When the murderers arrive, he reads their warrant (issued in the name of the King), and exits with the Keeper, who disobeys Clarence's request to stand by him, and leaves the two murderers the keys.
Clarence wakes and pleads with the murderers, saying that men have no right to obey other men's requests for murder, because all men are under the rule of God not to commit murder. The murderers imply Clarence is a hypocrite because, as one says, "thou ... unripped'st the bowels of thy sovereign's son [Edward] whom thou wast sworn to cherish and defend." Trying to win them over by tactics, he tells them to go to his brother Gloucester, who will reward them better for his life than Edward will for his death. One murderer insists Gloucester himself sent them to perform the bloody act, but Clarence does not believe him. He recalls the unity of Richard Duke of York blessing his three sons with his victorious arm, bidding his brother Gloucester to "think on this and he will weep." Sardonically, a murderer says Gloucester weeps millstones – echoing Richard's earlier comment about the murderers' own eyes weeping millstones rather than "foolish tears" (Act I, Sc. 3).
Next, one of the murderers explains that his brother Gloucester hates him, and sent them to the Tower to kill him. Eventually, one murderer gives in to his conscience and does not participate, but the other killer stabs Clarence and drowns him in "the Malmsey butt within". The first act closes with the perpetrator needing to find a hole to bury Clarence.
Richard uses the news of Clarence's unexpected death to send Edward IV, already ill, into his deathbed, all the while insinuating that the Queen is behind the execution of Clarence. Edward IV soon dies, leaving as Protector his brother Richard, who sets about removing the final obstacles to his accession. He has Lord Rivers murdered to further isolate the Queen and to put down any attempts to have the Prince crowned right away. He meets his nephew, the young Edward V, who is en route to London for his coronation accompanied by relatives of Edward's widow (Lord Hastings, Lord Grey, and Sir Thomas Vaughan). These Richard arrests, and eventually beheads, and then has a conversation with the Prince and his younger brother, the duke of York. The two princes outsmart Richard and match his wordplay and use of language easily. Richard is nervous about them, and the potential threat they are. The young prince and his brother are coaxed (by Richard) into an extended stay at the Tower of London. The prince and his brother the duke of York prove themselves to be extremely intelligent and charismatic characters, boldly defying and outsmarting Richard and openly mocking him.
Assisted by his cousin Buckingham, Richard mounts a campaign to present himself as the true heir to the throne, pretending to be a modest, devout man with no pretensions to greatness. Lord Hastings, who objects to Richard's accession, is arrested and executed on a trumped-up charge of treason. Together, Richard and Buckingham spread the rumour that Edward's two sons are illegitimate, and therefore have no rightful claim to the throne; they are assisted by Catesby, Ratcliffe, and Lovell. The other lords are cajoled into accepting Richard as king, in spite of the continued survival of his nephews (the Princes in the Tower).
Richard asks Buckingham to secure the death of the princes, but Buckingham hesitates. Richard then recruits James Tyrrell, who kills both children. When Richard denies Buckingham a promised land grant, Buckingham turns against Richard and defects to the side of Henry, Earl of Richmond, who is currently in exile. Richard has his eye on his niece, Elizabeth of York, Edward IV's next remaining heir, and poisons Lady Anne so he can be free to woo the princess. The Duchess of York and Queen Elizabeth mourn the princes' deaths, when Queen Margaret arrives. Queen Elizabeth, as predicted, asks Queen Margaret's help in cursing. Later, the Duchess applies this lesson and curses her only surviving son before leaving. Richard asks Queen Elizabeth to help him win her daughter's hand in marriage, but she is not taken in by his eloquence, and eventually manages to trick and stall him by saying she will let him know her daughter's answer in due course.
The increasingly paranoid Richard loses what popularity he had. He soon faces rebellions led first by Buckingham and subsequently by the invading Richmond. Buckingham is captured and executed. Both sides arrive for a final battle at Bosworth Field. Prior to the battle, Richard is visited by the ghosts of his victims, all of whom tell him to "Despair and die!" after which they wish victory upon Richmond. He awakes screaming for "Jesu" to help him, slowly realising that he is all alone in the world, and cannot even pity himself.
At the Battle of Bosworth Field, Lord Stanley (who is also Richmond's stepfather) and his followers desert Richard's side, whereupon Richard calls for the execution of George Stanley, Lord Stanley's son. This does not happen, as the battle is in full swing, and Richard is left at a disadvantage. Richard is soon unhorsed on the field at the climax of the battle, and cries out, "A horse, a horse, my kingdom for a horse!" Richmond kills Richard in the final duel. Subsequently, Richmond succeeds to the throne as Henry VII, and marries Princess Elizabeth from the House of York.