The Door Bell Rang — Rex Stout

There's no one or nothing the great detective Nero Wolfe wouldn't take on if the price was right. That's something wealthy society widow Rachel Bruner is counting on when she writes him a check for a whopping hundred grand. But even Wolfe has a moment's doubt when he finds out why the prize is so generous. For the oversize genius and his able assistant Archie Goodwin are about to lock horns with the FBI--and these highly trained G-men have a way with threats, tails, and bugs that could give even sedentary sleuth Nero Wolfe a run for his money.