Escape Dead Island

This can be found when you are on your way to Devan at the Marina Dock. You will come into a courtyard you will have previously traversed at the beginning of the game. The room in the middle of this courtyard will have a zombie inside that will burst out once you get close enough. Simply kill the zombie and the Grappling hook is inside.

I take no credit for the following solution. I copied and pasted it from PlayStationTrophies.org.

"Story related, cannot be missed.

You will acquire the grappling hook in Mission 8. As you make your way down the road into the Docks, there will be a small building directly in front of you with a yellow cross on the door. When you get close, it will burst open, and a zombie will emerge. Kill the zombie and then go into the room, and the grappling hook will be on the table next to the radio".

In addition I would just like to add that before you get to the door with the yellow cross there will be a butcher ahead of you and I would highly recommend stealthily taking him out first. If he spots you take a step back and he will go back on the ground and he will change his position, rinse and repeat and he will eventually have his back to you.