How did Jim become a prisoner of the Squire and Dr. Livesey?

From the text:

It was longer than the squire imagined ere we were ready for the sea, and none of our first plans—not even Dr. Livesey's, of keeping me beside him—could be carried out as we intended. The doctor had to go to London for a physician to take charge of his practice; the squire was hard at work at Bristol; and I lived on at the hall under the charge of old Redruth, the gamekeeper, almost a prisoner, but full of sea-dreams and the most charming anticipations of strange islands and adventures.