You may apply whatever rules you wish about who gets to use the key, or a key, but such a solution would prevent this problem from happening again.
The purpose is to keep Tom from watching TV when he’s supposed to be doing something useful, so his having a key to the lock would be Fail.
On the top shelf of a six-foot bookcase, there is a copy of “The Southern Harmony,” the shape-note hymnal. This book is shorter in height than its front-to-back length; taller books are on either side.
There, atop “The Southern Harmony,” pushed all the way to the back of the shelf, was the missing key-ring. A passing squirrel? A curious jackdaw? Poe’s raven? No, it must have been Frank, who can reach the top shelf if he stands on a chair, then steps on the slightly higher shelf ...
Unnngh.