A summer sequence follows youths connected with an industrial school and local boat-builders as they encounter burglars, a nocturnal explosion, storms, and other maritime dangers while learning to sail. The narrative balances episodes of detection, small-scale combat at sea, and strategic subterfuge with detailed, practical instruction in building, rigging, steering, and handling a sloop. It contrasts earnest, disciplined young men and more reckless associates, depicting efforts to reform the latter and stressing courage tempered by prudence. Hands-on practice, steady duty, and moral steadiness are presented as essential to becoming competent and responsible boatmen.