Sylvester the freeloader and Junior, as ship’s cats. Aboard a cruiser, Sylvester and his son go mouse hunting. Dad tries to goof off on the pretence that “You’re a little cat, so you take care of the little mice. I’m a big cat, so I take care of big ones, if any come along. Fair enough?” In the hold, a little mouse runs into a cage marked “Baby Kangaroos,” and Junior unknowingly releases Hippety Hopper, the kangaroo who looks like a “great giant mouse.” Sylvester Junior resorts to tap dancing to trap the creature inside his crate; the elder Sylvester contends with a real mouse made near-invincible by vitamins.