The Z-Stacks must share the up-river jobs with the Star Tugs. When a tramper that Zorran and Zug are towing goes out of control blocking the river and trapping the Stars, Zorran tries to take advantage of the situation to get more work for the Z-Stacks. However, Zorran's scheme does not go as he planned.

Warrior had always had a reputation for being a bit clumsy, but on this day he sets out to prove to Captain Star that he is capable of working without causing accidents. However, on his usual trips between the quarry and the old quayside he is as clumsy as ever and is told to report to Captain Star to answer to the many complaints about the damage he has caused. On his way to see Captain Star, he hears that Ten Cents is in danger, so he goes to help him straight away. The day has been a disaster so far but will it end that way?

It has been one of the hottest weeks of the summer. In such hot weather, there was a greater danger that ships might be carrying diseases. If this was the case, the ships would have to go into quarantine for several days and wait out in the estuary, away from the harbour. Under no circumstances should any of the tugs go near the ships in quarantine. Ships in quarantine fly the yellow flag. When the old tramper, Nantucket, lowers its flag, a great deal of confusion is caused and only wise old O.J. understands why.

An old dirty tramper from Australia suspected of smuggling lurks outside the limits of Bigg City bay. It is the notorious Johnny Cuba. When bad weather suddenly comes, he forces Zebedee, one of the Z-Stacks, to tow him into the safety if the harbour and into hiding. Normally, Zebedee would have been glad to help out an old friend but this time - things are different.