Donald Duck is working for Scrooge McDuck by cleaning his office, and Huey, Dewey and Louie are helping him.
When they are working, Scrooge notices that Donald can tell Huey, Dewey and Louie apart from each other despite them looking almost completely identical.
Scrooge seeks to exploit this ability by hiring Donald as a quality inspector in his factories.
There it is revealed Donald's skill only works on a subconscious level, and he causes multiple accidents on the job.
Any large catastrophic results are avoided, but Donald decides he has had enough and feigns that he has lost his sharp eyesight, in order to return to his normal, safe job.