So Evil My Love (1948)

Olivia Harwood, missionary's widow, meets charming Mark Bellis, artist and rogue, on the ship taking them both back to 1890s London. After Olivia opens a lodging house, Mark becomes her lodger then her lover. Olivia falls so completely under amoral Mark's spell that he's able to overcome her scruples, and soon she's his willing tool in an ambitious scheme of theft and blackmail...maybe too ambitious.