The secret detectives by Ella Risbridger

When Isobel Petty is orphaned, she finds herself being taken away from her home in India and sent to live with a distant uncle in England. On board the S.S. Mariana, she witnesses a shocking act – somebody being thrown overboard in the middle in the night. But when the ship’s captain insists that nobody is missing, Isobel and her two new reluctant friends must solve two mysteries – the identities of both the murderer and the victim – before they reach England and the culprit has the chance to escape.