Ten-year-old Michael and his family have recently moved into a decrepit house on Falconer Road. He and his parents are anxious, as his new baby sister was born earlier than expected and may not live due to a heart condition. When Michael goes into the garage, he finds a strange emaciated creature hidden amid all the boxes, debris and dead insects. Michael assumes that he is a homeless person, but decides to look after him and gives him food. The man is crotchety and arthritic, demanding aspirin, Chinese food menu order numbers 27 and 53, and brown ale. Michael hears a story that human shoulder blades are a vestige of angel wings.
Meanwhile his friends from school become more and more distant as Michael stops attending school and spends less time with them. He meets a girl named Mina from across the road and over the course of the story they become close friends. Mina is home-schooled. Nature, birds, drawing and the poems of William Blake interest her. She takes care of some baby birds who live in her garden and teaches Michael to hear their tiny sounds. Michael decides to introduce her to the strange creature.
Michael asks about arthritis and how to cure it, talking to doctors and patients in the hospital where his baby sister is being treated. Grace, an old woman, took a run through the hospital and came to see him. Once Michael returns to the hospital. he finds out that Grace has died. The creature whom Michael had moved from the garage—revealing a pair of wings at his shoulders—introduces himself as "Skellig" to Michael and Mina.
Michael's baby sister comes dangerously close to death, necessitating heart surgery. His mother goes to the hospital to stay with the baby and, that night, "dreams" of seeing Skellig come in, pick the baby up, and hold it high in the air, saving her. He subsequently moves from the garage after saying goodbye to Michael and Mina, answering their questions about his nature by saying that he is 'something,' combining aspects of human, owl and angel.
The baby, after a while establishing what she was going to be called, they settled on Joy, after thinking about calling it Persephone.