You must have Pet Pal for this quest.
Speak to the cat Unsinkable Sam by the fireplace in the Cyseal Inn. He'll tell you he loves Maxine, who lives in the Mayor's house. However, she's been rejecting his advances. Sam needs his old collar back before he can win her over.
The crab Source Nightmare in Black Cove drops Sam's Collar. Take it back to him and he will immediately go to Maxine, where she agrees to marry him. After they run off to purr by the fire, the player characters will have a conversation: