Murder Takes a Vacation by Laura Lippman

Muriel Blossom is both excited and nervous about her forthcoming vacation and cruise in France, and is charmed when a handsome man at the Baltimore airport befriends her as they are upgraded to first class. Since her husband died, she hasn’t looked at another man, but Allan is outgoing and attentive. When it seems as if she won’t make her connection at Heathrow, he insists she accompany him to London to spend the day, helps her get a hotel room, and book the Eurostar for the next day.