Dragons in the Water

Dragons in the Water by L'Engle, Madeleine. mass_market edition. ISBN: 9780440917199.

A stolen heirloom painting...a shipboard murder...Can Simon and the OKeefe clan unravel the mystery? Thirteen-year-old Simon Renier has no idea when he boards the M.S. Orion with his cousin Forsyth Phair that the journey will take him not only to Venezuela, but into his past as well. His original plan--to return a family heirloom, a portrait of Simon Bolivar, to its rightful place--is sidetracked when cousin Forsyth is found murdered. Then, when the portrait is stolen, all passengers and crew become suspect. Simons newfound friends, Poly and Charles OKeefe, and their scientist father help Simon to confront the danger that threaten him. But Simon alone must face up to his fears. What has happened to the treasured portrait? And who among them is responsible for the theft--and the murder?