The very first quest in How to Fish is the Who stole my beer quest that begins right after the tutorial. In this quest, you’ll have to help the Lighthouse Keeper, but he doesn’t tell you the exact steps (apart from the sparse hints).
In this guide, I will explain the process and also reveal the identity of the culprit.
How to complete Who stole my beer in How to Fish
The quest begins when you speak with the Lighthouse Keeper after completing the tutorial. First, you have to purchase a Beer Can for $12. Just buy one because you don’t need to get anything extra.

To get the Empty Beer Can as a lure, select the Beer Can from your inventory. Next, throw it to the Lighthouse Keeper, and he will hand you an empty can.

With the empty can equipped as a lure, start fishing. Unlike the traditional lures, this will catch the Spider Crab, which is your killer. Your real test begins once you reel in this monster.

The Spider Crab is not your ordinary crustacean. You can’t punch and kill it (I tried it, died, and lost all my money). Before you reel it in, you’ll need to have a knife. If you’re playing in a co-op lobby, the job will get easier. The Brass Knuckle also helps, but having the Knife is better.
Once you kill the Spider Crab, bring the carcass to the Lighthouse Keeper, and it will get the quest done. If you’re looking to complete more achievements in the game, have a look at this guide.