Tom Andersley returns to his family estate in Yorkshire after serving in France throughout the Great War of 1914-18, but like many of his fellow survivors he finds the estate very different and is not the same man who departed: a victim of "shell shock." Unable to reconnect with his wife and daughter, who have endured traumatic experiences of their own, he retreats obsessively into his old hobby, entrenching himself in his greenhouses in order to carry out meticulous experiments in the cross-breeding of fruit trees. He is interrupted in his existential paralysis by the mysterious arrival of an old friend from Eton, Lawrence Oates, whom everyone believes to be dead, having walked out of Robert Scott's tent in an Antarctic blizzard in 1912 in order not to slow down his companions in their doomed attempt to reach safety. Oates tells Tom that he was picked up and preserved by mysterious alien entities that have been entrenched in the Antarctic ice for millions of years, engaged in a long war fought with biological weaponry, against equally-mysterious adversaries, unknown to humankind, recent arrivals of their battlefield. Having learned about Tom's research from Oates, the aliens have sent the latter back to his homeland in the hope that Tom's expertise might enable him to bring a number of "seeds" to maturity, apparently as a clandestine move in their long-stalemated war. But what will the consequences be, for Tom, his family and humankind, of the failure or success of the mission into which he has been conscripted?