Ten Minutes Past Teatime by Elizabeth Chatsworth
A Victorian spinster-scientist and a Viking shield-maiden find passion and danger in dark-age Ireland.
1896: Forty-three-year-old scientist Miss Minerva Minett is determined to become the first female member of an exclusive inventor's club. To win their annual membership competition, she invents a time-traveling submersible, and launches her vessel into the Irish Sea for a quick trip to the dark ages. But when she sinks a Viking longship, accidentally joins a monastery raid, and falls into the arms of a grizzled shield-maiden, she discovers that time may not be on her side.