This is book number 6 in the Lord Peter Wimsey Mysteries (Audio) series.
Dashing detective Lord Peter Wimsey is caught up in the murder trial of mystery writer Harriet Vane. Her fiance has died of poisoning exactly as described in one of Harriet's novels-so naturally she is the prime suspect. As Peter looks on, he not only falls in love with the accused but eagerly helps with Harriet's defense when the first trial ends in a hung jury. Will she be convicted and executed for the crime, or can he save her life and win her hand in marriage? Strong Poison is the first of a series of Lord Peter Wimsey and Harriet Vane mysteries in which their complex romantic relationship is revealed in detail. This superb classic was originally published in 1930.