Leo and the crew are ready to take on the nasty invader the Rusty Crayfish, a greedy invasive species that eats all the food and takes over the homes of native crayfish. Sayat and Christian get right in the stream with Toronto and Region Conservation Authority to search for the big crustacean and come across some other creatures along the way. When they also discover a native crayfish, there's only one thing left to do: Crayfish race!