"Tom Cringle's Log" is a maritime narrative that features a cast of characters navigating the complexities of life at sea during the age of sail. The protagonist, Tom Cringle, is introduced as a young and ambitious sailor who joins the British navy at thirteen. Through a series of adventurous escapades across various ships, he earns promotions for his bravery, eventually becoming a trusted commander by the age of twenty-three. Another significant character is Mary Palma, Cringle's cousin, whom he marries after his rise to the rank of commander, highlighting themes of personal relationships amidst naval duty.

The narrative also includes Obadiah, a pirate integral to Cringle's journey, whose fate serves as a cautionary tale of the pirate life. Captain Transom represents the camaraderie and social aspects of naval life, known for his friendly gatherings on the islands. Additionally, Francesco Cangrejo, a Spanish pirate facing execution, adds depth to the story, emphasizing themes of loyalty and love as he entrusts Cringle with tokens for his betrothed. Together, these characters illustrate a rich tapestry of adventure, loyalty, and the harsh realities of maritime life.