The S/S Vellamo heads to Alexandria with Kaarina, the daughter of the ship's owner Hallerman, on board. As Kaarina trades places with the family's housekeeper Marja, first mate Yrjö takes a liking to Marja whom he believes to be miss Hallerman. Meanwhile Kaarina, pretending to be a member of the cleaning staff, starts getting close with lower ranking officer Kalle Aaltonen.