Captain Blood by Rafael Sabatini

The protagonist is the sharp-witted Dr. Peter Blood, a fictional Irish physician who had had a wide-ranging career as a soldier and sailor (including a commission as a captain under the Dutch admiral De Ruyter) before settling down to practice medicine in the town of Bridgwater in Somerset.

The book opens with him attending to his geranium whilst the town prepares to fight for the Duke of Monmouth. He wants no part in the rebellion, but whilst attending to some of the rebels wounded at the Battle of Sedgemoor, Peter is arrested. During the Bloody Assizes, he is convicted by the infamous Judge Jeffreys of treason on the grounds that "if any person be in actual rebellion against the King, and another person--who really and actually was not in rebellion--does knowingly receive, harbour, comfort, or succour him, such a person is as much a traitor as he who indeed bore arms."

The sentence for treason is death by hanging, but King James II, for purely financial reasons has the sentence for Blood and other convicted rebels commuted to transportation to the Caribbean, where they are to be sold into slavery.

Upon arrival on the island of Barbados, he is bought by Colonel Bishop, initially for work in the Colonel's sugar plantations but later hired out by Bishop when Blood's skills as a physician prove superior to those of the local doctors.