Widow Jennifer Nelson (Doris Day) works as a tour guide at a space research center, where she runs into scientist Bruce Templeton (Rod Taylor) only days after he hooks her mermaid suit with a fishing rod. Attracted to Jennifer, Bruce gives her an assignment to get close to her, and pretends he's working on something called Project: Venus. In truth, he has developed a device called Gizmo. Some of Bruce's associates, such as his partner, Zach (Dick Martin) and General Bleecker (Edward Andrews), are convinced Jennifer is a Russian spy who's after the secret plans for Gizmo. This leads into all sorts of complications, some of which are quite funny, and others not so much. Instead of doing The Graduate, which might have led into more mature and serious roles for Day, she did stuff like The Glass Bottom Boat, which made use of her talents as a comic actress (although not on a Lucille Ball level) but little else. Still, she's good in the picture, as is her co-star Rod Taylor, who handles the silliness with aplomb after already appearing with Day in Do Not Disturb. The movie tries to tie into the spy trends of the period with gadgets and the like, and Robert Vaughn of The Man from U.N.C.L.E even shows up for literally a second. Martin, Andrews, and Dom DeLuise [Fail-Safe] adeptly add some fun to the proceedings, although Paul Lynde [Bye Bye Birdie] is given the single funniest moment, which is the priceless expression on his face when he observes Martin and Andrews inadvertently in bed with one another. He also does a comical drag routine, especially when he's interacting with Day in a ladies room. Alice Pearce [The Belle of New York] and George Tobias play Day's neighbors, and essentially essay the same roles as the ones they play on TV's Bewitched, which debuted two years earlier. Arthur Godfrey is cast as Day's father, who owns the titular boat and has his daughter playing mermaid now and then to justify the title; he adds nothing to the picture. The movie is about half an hour too long, and hasn't enough of director Tashlin's trademark cartoon-like humor, although there are some amusing scenes such as a comical encounter between Day, DeLuise, a cake, and a trash can. It's amazing that nobody noticed that the song sung over the opening credits, "The Deep Blue Sea," is basically a knock-off of "Mockingbird." This was the last of Day's films to make money, after which she fled to television.
Verdict: Punctuated with enough laughs to keep you watching, but never a real riot. **1/2.