Answer:
"Off the hook” is an idiom, a literary device that means no longer having an obligation or responsibility to someone.
Step-by-step explanation:
Unlike a metaphor, an idiom´s meaning is more difficult to understand, as it can not be directly derived from the words. In this example, the understanding of the idiom requires some knowledge about how, in fishing, getting a fish off the hook means releasing it after having cathed it.