Mactaggart is the rascally skipper of the puffer The Maggie, a flimsy rust-bucket which hauls freight up and down the west coast of Scotland. When wealthy American businessman Calvin B. Marshall, General Overseas Manager of World-International Airways, wants to transport a precious cargo to his newly bought mansion on Kiltarra in the Western Isles, Mactaggart manages to trick Marshall's agent into hiring The Maggie for GBP300, a sum that might be useful for some much-needed repairs. Marshall learns that his valuable cargo is at risk in a vessel that's less than seaworthy, he does all in his power to have the valuable cargo transferred to a more reliable vessel. What Marshall is not prepared for is the wily Mactaggart's sly delaying tactics and crafty machinations. What follows is a hilarious and unexpected journey that will have unforeseen consequences for everyone involved ...