Thomas and the Billboard - S12-E1
Other mistake: In the opening scene when Edward and Henry can be seen going into Knapford, Henry is wearing Gordon's face mask.
Other mistake: Henry was supposed to take Emily's trucks to the Coaling Plant, but he takes them to Knapford Yards instead. The narrator also refers to Knapford Yards as the Coaling Plant.
Answer: He was in the water.