Henry and Hiro fill up their tenders with coal because they are collecting very heavy trucks from the Quarry to take to the Docks. After collecting the trucks, they start puffing black smoke. Duck sees this and suspects that they have got some of the bad coal. Henry is worried, and wants to wait for the good coal Duck is fetching, but Hiro disagrees. He says they can keep puffing with the bad coal. Despite this, Henry goes back to the shed to wait for good coal.

The load is too heavy for Hiro alone, so he leaves half the train in a siding so he can deliver that later. He passes Gordon who is grumpy because of Hiro's smell. When Hiro arrives at the Docks with the first row of trucks, Thomas comments on the smell, but Hiro ignores him and goes to fetch the last trucks.

Hiro delivers the last trucks to the Docks, where Sir Topham Hatt is waiting. He tells Hiro to go to the Smelter's Yard to collect some iron beams for a ship. He states that they are very heavy. Hiro is worried because of the bad coal, but he does not want to say no to Sir Topham Hatt.

Hiro puffs to Tidmouth Sheds to find Henry. He says that he needs help with another job. Henry is admired that Hiro has delivered all the heavy trucks to the Quarry without help. It inspires him to keep on puffing, so he agrees to help Hiro with the iron beams. They go to the Smelter's Yard to collect them.

Hiro and Henry puff on, but Gordon's Hill proves to be too much for Hiro, and he breaks down. But Henry is determined, and he pushes them all the way to the Docks. Sir Topham Hatt is very pleased that they managed to keep puffing, even with bad coal. As a reward, Henry and Hiro get their fireboxes fixed and are filled with new, clean coal.