THE MIGHTY CELTDonal lives with his single mother, Kate, in Belfast. After school, Donal helps a dog trainer named Good Joe to look after his racing greyhounds. Donal is good with dogs and knows just how to handle them. And thats why, as soon as he sees The Mighty Celt he knows exactly what this dog is capable of. Good Joe is not so sure, but nevertheless makes Donal an offer he cant refuse: the boy can train the dog and, if Mighty Celt manages to win three races in a row, Donal can keep him.
The Mighty Celt and Donal set to work. But something else is preoccupying Donal, namely, the recent reappearance of O. At first, he is not at all happy about the way this mysterious figure from the past plays on his mind. But then the two develop a liking for each other and, after a while, even Kate and O slowly find themselves drawn to each other again. Good Joe, however, is the only one who makes no secret of his dislike of O.
In fact, Good Joe detests everything that O stands for and is not at all pleased to observe the growing friendship between O and Donal. Os return makes Good Joe so angry that he even reneges on his agreement with Donal a decision that threatens to overturn everything Donal believed in.