Shadow of the Rope

From Google Books: "Rachel Minchin stands in the dock, accused of murdering the dissolute husband she was preparing to leave. The trial is sensational, and public opinion vehemently and almost universally against her. When the jury astonishes and outrages the world with a vedict of Not Guilty, Rachel quickly finds herself in need of protection. It comes in the form of a surprising offer of marriage from a mysterious stranger who has sat through every day of her trial.

The marriage to this intriguing stranger, Mr. Steel, is by mutual agreement to be a platonic one, the only condition of which is that neither is ever to question the other about the past. The two travel to Steel's remote country estate, where Rachel accidentally discovers that her second husband's past was somehow intertwined with her first husband's history - but how, exactly, and why he determined to marry her, Steel will not say. As her doubts about her husband increase, local busybodies threaten to unearth Rachel's own past. And that is the least of the secrets that comes to light as this entertaining mystery unfolds."