Momo and Dodo are eight-year-old twins, sister and brother, who live with their mom and dad and their faithful dog Brownie. Momo and Dodo's young lives are full of adventures, each of which teaches them a lesson.

In this adventure, Momo goes fishing with her dad on his boat out on Lunker Lake. Their plan is to catch a fish big enough to take home for dinner. Momo catches one fish, and then another, but asks her dad to put both fish back into the lake. Momo wants to catch the lunker that gave Lunker Lake its name.

Momo hooks what feels like a huge fish. The fish is so big that Momo cannot reel it in. As Momo struggles with the fish, a storm moves in and it begins to get dark. Will Momo catch the big fish? Is it the lunker? How do Momo and her dad find their way to shore and back home in the dark? Is Brownie the hero? What lesson does Momo learn on Lunker Lake? It is an adventure that Momo will never forget!