Right now, spacecraft are circling Mars, sweeping over Terra Sabaea, Syrtis Major, the dunes of Elysium and Mare Sirenum - on the brink, perhaps, of a discovery that would inspire humankind as much as any in our history. With poetic precision, Sarah Stewart Johnson traces the evocative history of our explorations of Mars, interlacing her personal journey as a scientist with tales of other seekers who have scoured the planet for signs of life. Ultimately, she shows how its story is also a story about Earth: it is a foil, a mirror, a tell-tale reflection of our own anxieties and yearnings to find - if we're lucky - that we're not alone.