*onto someone
seeing through someone's deception. (*Typically: be ~; get ~; catch ~.) By the time we got on to the con artists, they were out of town. The sheriff got onto Jed, and Jed wanted to get out of town fast.
*onto something
1. Fig. alerted to or aware of a deceitful plan. (*Typically: be ~; catch ~.) The cops are onto your little game here. Fig. having found something useful or promising; on the verge of discovering something. (*Typically: be ~; get ~.) I think we are really onto something this time. lam onto a new discovery.