All the conspiring to kill King Duncan comes from Lady Macbeth. When Macbeth returns home after the battle, and after he has been awarded the title of Thane of Cawdor by the King, and after he has written to his wife about the witches prophecy that he would become king, Lady Macbeth learns that King Duncan is coming to their home for a visit that evening.
Lady Macbeth then hatches the plot to kill the king while he is a guest in their home. Macbeth is manipulated into the murder by his wife.
First she must get the guards, who sit near the king's chamber, drunk. Then she will take the daggers from the guards and leave them in the king's room. Once she does this she will ring a bell to signal her husband that all is ready. Macbeth will kill the king with the guards daggers.
After Macbeth commits the murder, he returns to Lady Macbeth, she asks whether he remembered to put the bloody daggers back with the guards to frame them for the murder. He says no. She tells him to go back and get the daggers from the king's room, he refuses because he is a nervous wreck and already feeling terrible guilt. So Lady Macbeth must retrieve them and plant them on the guards. She then tells her husband who looks at his bloody hands with fear and disgust, to simply wash them with a little water to wipe away the blood and the deed itself.
Macbeth has the idea of the murder put into his head by the witches, but he is hesitant about going through with it. He sends a message to his wife telling her what the witches have said and also communicating his misgivings. His wife, who has a poor opinion of her husband's initiative, immediately becomes a strong proponent of the murder. She overrides Macbeth's scruples (which were never very strong) and the two of them decide to murder the king while he is staying at their castle that night.
When the time for the murder comes, Macbeth is nearly paralyzed by his conscience, and has hallucinations of a bloody dagger in the air. His wife, realizing that there is no going back now, forces him to finish the deed and herself goes back to the murder scene to establish an alibi by smearing the king's servants with blood. Nevertheless, she is acting beyond her natural limits, as evidenced by her comment about how much the king’s sleeping form reminded her of her father.
After the murder is discovered, both the Macbeths manage to pretend it is a surprise to them. Macbeth kills the grooms to prevent them explaining their innocence, and Lady Macbeth faints at a critical moment to distract the onlookers. Through the close and interactive cooperation of both Macbeth and his wife, the plot thus attains a temporary success, with the king’s sons frightened into flight and Macbeth, for the time, secure on the throne.