Book 2 of the Adventures for Girls series.
Three young, female college students manage to get free housing aboard a friend's luxury yacht, the O Moo, that's in a Chicago dry dock. Fortunately for them, they have much experience in dealing with fearful situations and mystery, because these things seem to follow them around. A threatening note, a terrifying blue face, even being set adrift in a harrowing winter storm all work together to test their courage and resourcefulness, and eventually lead to peace.
(Summary by Keith Salis)