As London is submerged below flood waters, a woman gives birth to her first child, Z. Days later, she and her baby are forced to leave their home in search of safety. They head north through a newly dangerous country seeking refuge from place to place, shelter to shelter, to a desolate island and back again. The story traces fear and wonder, as the baby's small fists grasp at the first colors he sees, as he grows and stretches, thriving and content against all the odds.