“Since Louise got her hooks into Paul, she hasn’t let go!”
Back in the days of pirates, getting your hooks into something meant literally latching onto a ship with a grapnel, the grappin above. Al the buccaneers had to do was toss it aboard their target for attack and pull on the attached rope to get close. Then it was easy for them to board the other ship, surprise their prey, neutralize them and take all their booty.
We now use this expression for a situation where someone has taken control over a person or a thing, is monopolizing it and won’t give up control.