Michael, who is ten years old, and his parents have recently moved to a dilapidated house in Falconer Road. While they work on renovating the house, Michael's sister is born prematurely. Due to her critical heart condition, it is not sure whether she will survive. Michael deeply cares about her, so this situation puts him under an extraordinary amount of stress.
He is also startled by the discovery of a filthy homeless man in the garage, who seems to be rotting away between dusty items. However, Michael does not tell anyone about the man; instead, he provides him with the two things he craves most: Chinese food and beer. Michael learns that the man suffers from arthritis and is therefore unable to move.
At the same time, Michael’s school friends drift apart from the boy, who stops coming to school and spending time with his friends to help his father at home. He gets acquainted with a girl called Mina, who lives further down the road. Mina is homeschooled and interested in nature, painting and the poems of William Blake. The girl looks after the birds living in her garden, and she shows Michael the beauty of nature. Michael eventually decides to let her meet the strange man in the garage.
The man gradually warms up to the two children, who nurture him and bring him to an abandoned house to keep him safe. They discover his wings, giving them the idea that he is an angel. He also reveals his name: Skellig. Apart from Michael and Mina treating Skellig's arthritis by giving him cod liver pills and aspirin, the owls in the abandoned house provide him with food.
With his strength regained, Skellig performs a magical dance with Michael and Mina, which causes the three to become one. At the end of the dance, wings briefly appear on Michael's and Mina's backs.
Finally, on the day of the baby's heart surgery Michael is understandingly restless and has visions of his sister dying, while Mina and her mother try to give him hope. Indeed, against all odds, the baby survives. Michael's mother later recalls a dream where an angel danced with the baby, giving her wings, which leads to her revival.
In the end, Skellig bids farewell, still leaving the children puzzled about his true nature. Michael promises to take good care of his sister and to protect her.