Someone (August West?) mentioned Dead Man's Tide in a comment on a long-ago post, so I thought I'd grab my copy and read it. My guess would be that Day Keene aimed this book right at Gold Medal, but it missed the cut.
The opening is one that's been used many times before. Charlie Ames wakes up in a strange place with no memory of the night before. There's no dead body around, as there often is in this kind of story, but he sees a lot of blood. The body shows up, however; Ames is accused of murder, and the frame is a perfect tight fit. Even his wife doesn't believe he's innocent at first. When she does believe him, she searches for evidence to clear him. Finding something, she's knocked out and accused of a second murder.
Things happen fast, as you'd expect in a Keene novel, and if the gimmick is too obvious, there's a lot of Florida local color (both scenery and characters) to make up for it. The book was later republished by Avon as It's a Sin to Kill under the Keene byline. Check it out.