It is the day of the lowest tide of the year, and Captain Star's seven tugs are all hard at work to get everything done before the tide makes movement around the harbour too difficult. Hercules is away guiding an ocean liner into port, and Big Mac, O.J., and Sunshine are working upriver at Mittsville, hurrying to get cargo moved downstream. Only Ten Cents, Top Hat, and Warrior are working in the harbour itself. Captain Star calls Ten Cents and Top Hat to the pier and orders them to bring in a large steamer, loaded with cargo that was having engine trouble. It is very dangerous work, but the tugs were determined. As the two tugs head out to open sea, Zorran, leader of the Z-Stacks, was watching them, wondering what they are up to. In a state of curiousity, Zorran keeps a safe distance behin