American Girl Samantha Mysteries Series by Sarah Masters Buckey

Samantha is excited about her family's stay at a fancy new "apartment-hotel" - until she learns there's a terrible curse on the building's owner! As soon as Samantha arrives, one thing after another goes alarmingly wrong. Is it the curse - or is something else scaring the residents from Ravenscourt?

Samantha and Nellie set sail for Europe in 1906. Also aboard the ship is a world-famous archaeologist and the legendary sapphire he is carrying to a London museum. When his priceless jewel disappears, Samantha realizes that every one of the first-class passengers is a suspect--and one of them must be the thief!