Hooks aren't just for the beginning. Smart writers always have a hook at the end to make the reader want to buy the writer's next story.
The final hook is the fulfilled promise of the story. If the story is a romance, the story should end with the promised "happily ever after." In a mystery the crime is solved or justice is meted out, and in a fantasy the quest is achieved or the monster defeated. Science fiction as a genre doesn't have such an obvious promise, but the individual story has a goal which must be reached.
A "warm fuzzy" scene that offers the reader a happy emotional feeling for the main character or characters often acts as the final hook. Warm fuzzies are the scene of domestic bliss with the hero and heroine holding their baby, or the traveler returning home to family, or the adventure companions sharing a laugh and a beer.
If a warm fuzzy doesn't fit the tone of the story, an extremely powerful and emotional final scene is the most effective hook possible. The reader will read the end, sit quietly for a short time, then mutter to himself, "Damn that was good," and he'll wait eagerly for the writer's next story.