Boundless McLennan, a young Scottish printer, is sentenced to indentured servitude in the American colonies. Upon landing in the New World, he escapes and learns of a marvellous beast inhabiting the far western plains. To avoid recapture he assumes a new identity and secures employment on a shallop that travels up and down the Patapsco River ferrying cargo to farms and plantations. An itinerant trapper feeds his curiosity about buffaloes. He kills a gambler in self-defence and abandons the boat and his companions for fear of his real identity being discovered. He becomes lost in the immense wilderness but is saved through encountering Mose, a trapper.

Mose takes Boundless under his wing and seduces him with tales of endless grasslands beyond the Alleghenies where the buffalo are rumoured to be so plentiful that 'Jehovah himself could not count the heads'. Together, they set out on an epic adventure across a thousand miles of wilderness full of dangers-from bandits, wild animals, hostile Indians, and a brutal war between England and France for possession of the New World. Despite the perils of the journey, Boundless is determined to lay eyes on the mysterious creature that beckons him to his destiny on the vast, windswept plains.