At recess one day, sisters Elsie and Theo spy a nut wiggling on the ground. Out pops Bennythe world’s smallest and most gentlemanly walrus. After the girls learn that Benny misses his home in the sea, they send him sailing in a milk-carton boat, along with a trusty band of adventure-seeking slugs. Together, Benny’s Brigade (as they call themselves) begin their voyage to a truck-sized island paradise, avoiding the salt water as much as they can. Slugs don’t like salt.