Since the beginning of time, Favour, the mystical horse, had been coming to earth to rescue the victims of evil and injustice, using living people as messengers to carry out his work. People like Rose, at this special age when anything is possible. With the horse, she can transcend time and space to travel to other scenes in the past, present and future that were as real as her everyday life.

Rose is not having an easy summer. Her grandfather is ill, and her mother has been called away to look after him, leaving thirteen-year-old Rose and her clueless father to manage without her. This means taking control of the hotel her mother runs by the sea in the full clamour of tourist season--Rose has her work cut out for her. All this work gets in the way of riding with her friend Abigail, and sailing with Ben, an older boy that comes to stay at the hotel every summer with his father.

But her earthly woes are overshadowed by her duties as a magical messenger. She is transported through time by Favour, witnessing important clues that all lead up to an injustice that Rose must prevent. To make matters worse, the evil Lord of the Moor is trying to stop her with his ghostly army.

Cry of a Seagull is the last part of The Messenger fantasy series written by Monica Dickens.