Hargreaves was Harrison Chase's butler. He was very loyal to his master, even during Chase's more fanatical bouts of insanity. When Arnold Keeler began mutating into a Krynoid, Hargraves assisted Chase in carrying him to the cottage near the mansion, where they tied him to a bed. At Chase's instruction, Hargreaves fed the slowly transforming Keeler meat to accelerate his change. When Keeler completed his transformation, though, and broke free of his bonds, a terrified Hargreaves ran away, however he didn't join the mansion's guards in fleeing, instead remaining at Chase's side.
Despite his loyalty, he was killed; following Chase's descent into total madness as a result of his decision to assist the Krynoid, he allowed the Krynoid-controlled plants in his greenhouse to attack Hargreaves, Sarah Jane Smith and Scorby. Although the Doctor and Sergeant Henderson arrived in time to save Sarah and Scorby, they couldn't rescue Hargreaves, who was strangled to death by vines.