The Face-Changers by Thomas Perry

Jane Whitefield is settling in to married life, having given up her career as a “guide” by helping people disappear. But her husband, Dr. Carey McKinnon, asks her to do one last job—helping his mentor Richard Dahlman disappear. Dahlman has been arrested for murdering his physician partner, Sarah Hoffman. Both Jane and Carey know he's not guilty, but it appears that other people are after him besides the police. While aiding Dahlman, Jane also discovers that there are some other guides out there who are using her name and don't have their clients' best interests at heart. As time goes on, Jane worries for both her and Carey's future wondering if Carey will end up in jail. The Face-Changers is the fourth book in the series.