Macbeth and Banquos relationship isn't as good as it was before the witches prophecies about their future. Macbeth is especially distracted and wondering if it's true but Banquo wants to rid of his "cursed thoughts" and flees the country with his son, Fleance.
THE KING IS DEAD!!
Macbeth gets the signal off Lady Macbeth, knowing that was the time to murder King Duncan while he slept.. He prayed Earth "would not hear his steps" so he can commit the crime easily and guilt-free.
Macbeth returned but still had the bloody daggers with him, instead of 'planting' them on the bodyguards. Macbeth was already guilt-stricken and couldn't go back to place them, so Lady Macbeth did it instead. When she returns, Macbeth is panicking - “Will all great Neptune’s ocean wash this blood / clean from my hand?”
Macduff goes to wake the King after a night of strange events - the earth shook, birds were screeching but finds him dead, he then goes informing the servants in the castle, shocking them all.
Macbeth and Lady Macbeth enter and when they find out what has happened, Macbeth laments his death, says he wishes it was him and says he killed the guards whereas Lady Macbeth faints and collapses to the floor. Malcolm flees to England and Donalbain flees to Ireland as they might be at risk.
Macbeth's cousin Ross asks Macduff who he believes did it, he thinks it was most likely that the body guards did it but because Malcolm and Donalbain fled Scotland, they are suspicious of them too.