In the story, a strange phenomenon is gripping England. Common, everyday birds of all sorts are flying to the southern part of the country and flocking to towns and cities in immense numbers. Nat and his family experience this avian invasion firsthand when a flock of birds fly into his children's bedroom in a frenzy.
The birds proceed to attack the children, but Nat manages to push the children out of the bedroom. He then locks himself in and uses a blanket as a weapon to fight off the birds. The next day, he puts the dead birds (about fifty of them) in a sack and goes out to bury them. The ground is frozen solid, so he decides to bury them near the shore. However, as he is about to put them into the shallow grave he has dug for them, a strong gust of wind takes the birds. Nat decides that the dead birds will be drawn out to sea at the turn of the tide. He turns to go back home, but not before seeing tens of thousands of gulls floating and waiting on the waves.
In order to prevent more birds from coming into the house, Nat decides that he will board up the windows. He does this by hammering boards across all the windows in the house. As a precaution, he even goes out earlier than usual to meet his school age daughter (Jill) at the bus stop.
On the way home, Nat and Jill realize that the sky is darkened with birds. Worried, Nat asks Mr. Trigg, the farmer, to give the visibly frightened Jill a ride home. Nat advises Mr. Trigg to board up his windows that night, but the old farmer sees no need to do so. As he nears his house, Nat is viciously attacked by the birds. He decides to reinforce the sides of all the windows with wedges of old tin and strips of wood and metal.
Nat decides that the family will sleep downstairs, in case the birds breach the boarded up chimney and manage to get into the bedrooms. As night descends, the family hears the birds throw themselves against the windows and doors. Only an improvised, kerosene-fueled fire manages to beat the birds back out the chimney.
The next day, upon discovering the farmer (Mr. Trigg) and his wife dead in their farmhouse, Nat makes the decision to use some of the Triggs' groceries, reasoning that they would understand if they were alive. When the family return to their cottage, Nat decides that he will reinforce the window boards with barbed wire. This is his new scheme, but the story ends uneasily when Nat realizes that the hawks are ignoring the windows, concentrating instead on splintering the wooden door with their powerful talons.