Self-publishing was one of the big topics at this year’s Frankfurt Book Fair, and at least one self-publishing book caught the eye, and wallet, of a major publisher. In what is rumored to be a deal worth $500,000, Jennifer Brehl at HarperCollins’s William Morrow imprint bought North American rights to Tina Seskis’s novel, One Step Too Far.

The debut, which was originally published in April as a Kindle e-book, went on to hit #1 on Amazon. Seskis, who grew up in New Hampshire and now lives in London, followed the e-book publication with a paperback release, and that print edition went on to hit the bestseller list of the British bookstore chain, W.H. Smith.

One Step Too Far follows a lawyer named Emily Coleman who inexplicably abandons her life. Despite what appears to be an idyllic existence—a beautiful two-year-old son, a lovely home, an adoring husband—Emily wakes up one summer morning, grabs her passport, and hops on a train bound from London to Manchester. Determined to leave her old life behind, Emily meets a croupier named Angel who becomes her only new friend, and who also leads her into a dangerous new existence.

Brehl told PW that Seskis likes to refer to the book as a “whydunit,” because it leaves a host of questions about its heroine’s actions unanswered. The novel, which works up to a final secret-reveal, was something Brehl said she picked up one night and “didn’t put down until I finished it the next morning.”

John Elek, with the British firm United Agents, represents Seskis.