In Act 3, Macbeth becomes suspicious of Macduff and thinks that Macduff will try to overthrow him. Macduff has pulled away from Macbeth, so this arouses his suspicions. As a precaution, Macbeth hires servants to spy in the houses of Macduff. He says that he has not left any of the houses unaccounted for and that in each one there is a servant whom he pays to spy on Macduff and his family. Macbeth hopes that he will find out information that allows him to accuse Macduff of treason. Later, Macbeth goes back to the witches and learns that he should in fact beware Macduff, so his hiring servants to spy on Macduff was a good plan.