Recall Jim Hutton being on suspension at MGM and agreed to make this movie as a way to get his release from MGM. The studio involved contract stars Yvette Mimieux, George Hamilton and Hutton's one time leading lady Paula Prentiss in cameos. Note: MGM did not cast its other MGM stars George Peppard and Richard Chamberlain in this film considered a trifle as a Connie Francis film. Connie made one film a year for MGM and were all successes.
OK, I see JH played serious too. I originally made the observation when I saw him in Where the Boys are. That was at the time before Hanks was a "serious" actor. JH was playing comedy there. Not familiar with his work, I see here he did drama after WTBA. (and before that, just not in the movies). Upon further examination I see their careers paralleled beyond the light stuff.
They both started out in comedy. Hanks was lucky enough later in life to get great dramatic roles. Hutton's popularity went down and he wound up doing TV movies and Ellery Queen.
The one in this film who really stood out imo was Susan Oliver. What a hottie. She really should have had a much bigger career. No doubt she was successful in tv, but she could have done better in films.