"Two people can be moving together, relative to the rest of the world. And yet, relative to each other, they’re still."

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Sam’s really busy: applying for PhD in physics, babysitting her new nephew, and supporting her mum who’s going through chemo. When she bumps into up-and-coming novelist Paul on a train, she instantly feels like she’s met someone who can keep up with her.

Their relationship picks up momentum as they race through stations and milestones together. But is there an obstacle on the tracks?

Using Newton’s laws of motion as an unexpected lens through which to explore the forces that shape our lives, Stephanie Greenwood’s gripping new thriller is an exploration of love, trust, and what it takes to get off a train hurtling in the wrong direction.