The Adventure of the Wary Witness

Ellery's old college chum, Linville Hagen, is accused of murdering mobster Nick Danello, and Ellery must find a missing witness who can prove his innocence. This missing witness was a woman wearing a green dress - a description, of course, which could fit any woman in New York. Frank Flannigan comes along for the ride too, and this time he's not quite so antagonistic towards Ellery.