What does 2 Samuel 15:34 mean?

'But if you go back to the city and say to Absalom, "I'll serve you, just like I served your father," you can help me by undermining Ahithophel's advice.' 2 Samuel 15:34 - Modern Text Bible

(David asks Hushai to pretend loyalty to Absalom so he can secretly work against Ahithophel's plans from inside the city.)