The ship's captain held Henri LeFevbre as a slave/indenture cabin boy, for the latter to pay for the rest of his parent's crossing fee. One day, Moses and James Hiller found Henri behind bars in the lower part of the ship. They used a piece of the printing press to pry the jail cell. It was then they rescued Henri. Hiding him in a wooden crate full of hay, the slipped him right under the ship's captain's nose.
The ship's captain appears a retelling/flashback in The Intolerable Acts episode.