Ten-year-old Michael and his parents have recently moved to a dilapidated house on Falconer Road. While they work on renovating the house, Michael's sister is born prematurely. Due to her critical heart condition, it is not clear 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 and crotchety 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. He also feels something odd between the man’s shoulder blades—he thinks they might be wings.
At the same time, Michael’s schoolfriends drift apart from him. He stops coming to school and spending time with his friends, instead helping his father at home. He becomes 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. Mina 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 and Mina's backs.
On the day of Michael's sister's heart surgery, Michael is 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 led to her revival. The family decides to name the baby “Joy."
In the end, Skellig bids the children farewell, still leaving them puzzled about his true nature. Michael promises to take good care of his sister and to protect her.
