The snow has melted, but the thaw reveals a world transformed. London is in ruins, its population a fraction of its pre-freeze level. The weather has become wildly unpredictable - huge pressure swings leading to powerful localised storms. And this has led to an epidemic of migraine. When a storm hits, the pain comes, along with a wide range of visual and haptic hallucinations named Migraine 'aura'.

The novel starts with Ellis, one of a very small proportion of the population who don't suffer from weather-induced migraines, being struck by a migraine attack for the first time. After being blinded by hallucinations, he wakes in a ruined bookshop with its former owner, Sam, who pulled him to safety from the storm. No longer excluded from the migraine epidemic, Ellis decides to find his ex-girlfriend, Luna, and win her back. With Sam tagging along, he sets out from the bookshop and heads south.

From here, chapters alternate, giving the backstory of Ellis and Luna's relationship, from their first meeting to their final rupture, while in the present day the two men wend a crooked psychogeography through the centre of the city. Migraine is concerned with questions such as: what does a society look like, if it's organised around chronic pain? What kind of culture would this set of conditions produce?