As soon as Jones realized he could get in trouble if they reported him, he became putty in their hands.
putty in (one's) hands
Easy to control or bend to one's wishes. (Putty is a very malleable material.) Oh, come on, Julia is putty in our hands—we can definitely get her to help us with this prank.
*putty in someone's hands
Fig. [of someone] easily influenced by someone else; excessively willing to do what someone else wishes. (Putty is soft and malleable. *Typically: be ~; seem like ~.) Bob's wife is putty in his hands. She never thinks for herself.Jane is putty in her mother's hands. She always does exactly what her mother says.