After an encounter with a school of migrating tuna, the Octonauts discover that one of the speedy fish, Tina, has been left behind. And she's injured! Poor Tina has a hook stuck in her mouth and is too weak to swim. After Peso tends to her wound, the Octonauts agree to help get her to the tuna spawning grounds. But they'll have to be quick: egg-laying season doesn't last long. Luckily, Tweak's latest gup, the Gup-R, is the fastest she's ever built! The Octonauts use it to tow Tina, but when the Gup-R's battery dies, how will they catch up to the rest of her school?