Harold helps Percy deliver his mail, but Percy believes he is under threat. When he reaches a broken signal, he is forced to wait until the signal is fixed. He is even more upset when Harold comes to take his mail onward. Harold decides to take the mail all at once - with disastrous results.

Misty Valley is often very misty, which is why Cyril, a friendly fogman, puts detonators on the tracks to warn engines of oncoming mist. The Fat Controller replaces him with a fog horn, believing he needs a rest, but it turns out the fog horn is more trouble that it is worth.