If you’ve got a character whose uncle is a Scotland Yard detective, and he’s looking for a way to catch the same baddie that your character is dealing with, and your character tells him all about it in a confusing way while asking for help, it is highly unlikely (and unfair) to make the uncle totally ignore what the character was saying.
Look. Part of being a police detective is figuring out (often through careful questions) what people don’t know enough to tell you straight out. They are used to dealing with confusing stories. They are used to dealing with tiny hints. The whole thing should have made the uncle sit there for hours with the main character and take over the story, not send him off with a flea in his ear.
Furthermore, the main character in question might be a bit silly, but he received a lot of training in school on how to present information clearly, and how not to forget key information. In canonical stories, he’s shown to have a good memory and presence of mind. The scene makes no sense, even from fanfic standards. I literally don’t think I can stand any more.
Sigh. Why on earth not go for the obvious, and make the uncle unavailable? Send him off on a case to somewhere with no telephones, like someplace off in the Orkneys. Why not have the evil baddies’ web provided with someone at Scotland Yard being paid off, who pretends there’s nothing in the story and sends the person off with reasonable explanations and a flea in the ear?