Guild of Specialists, Book 1: Operation Red Jericho

A brother and sister find themselves in the care of their uncle, who is captain of a vessel anchored off the coast of China. Their parents are off doing some sort of research, and the kids have been kicked out of school after school. They aren't bad kids; rather they are curious and willing to risk. They find themselves embroiled in a dangerous plot after overhearing a conversation between members of the ship's crew. This action/mystery is geared to ages 9-12 , but a strong 8 year-old could handle it. This is a series so if your reader likes it, you can keep going!