Reminiscent of Celia Rees, first-timer Collison introduces orphaned Patricia Kelley, 17, who sneaks aboard a British merchantman headed for the West Indies, hoping to claim her father’s estate. When she discovers that she has few rights aboard ship or on land, she marries the ship’s physician, an “old” man of 34, as a matter of survival and despite her attraction to a low-ranking bosun’s mate. On and off duty as a physician’s assistant, Patricia witnesses warfare, “modern” medicine, birthing and early contraception and the women at sea who will later be forgotten by history. After her husband succumbs to yellow fever and she finds herself penniless, the young woman dresses like a man and enlists as a surgeon’s second mate on a frigate. Patricia’s new life could be a path to greater independence and reuniting with her true love. A few forced explanations (e.g., “Pleaded their bellies? You mean to say they were pregnant?”) can be overlooked in what is an otherwise well-researched, riveting adventure that brings to light an overlooked part of women’s history. (map, author’s note, glossary, sources) (Historical fiction. YA)