The Snapper takes them first to see Cuchulain. Cuchulain’s charioteer, Laeg, is the double of Sean O’Reilly, a school fellow to whom Nora is very attracted. They save the lives of two men, a sailor who has fallen overboard, when he sees someone struggling in the water, and the man whom he has seen, who has been thrown overboard from a pirate ship. The rescued stranger sees a knife which Laeg always carries. He tries to steal it, attacking Laeg ferociously. Before Jik and Nora can help Laeg, they are whisked back to their own time.

While looking up information in the library the next day, they meet up with Sean O’Reilly. Sean is clearly angry with them, but they have no opportunity to explain that they didn’t deliberately abandon him; and they are still not quite clear if he and Laeg are the same person.

The Snapper then takes them to meet St Patrick, where they help the young Patrick, who is a stowaway escaping from Ireland, but realise that they are still far too early in time to find out about old Peter’s invention. Sean turns up again, and this time Jik and Nora are able to help him fight off the stranger, who also appears; and who they discover is a druid. Sean explains to them that the knife came to him through his father, who purchased it abroad. The knife is the former property of a druid priest, and is considered sacred. There is a curse on anyone who uses it sacrilegiously. Sean’s father and mother were killed in a car crash last year, after his father used the knife in lieu of a screwdriver to change a wheel. Sean is determined to find out if the knife really had anything to do with his father’s death. The Snapper has been taking him back in time for that reason.

Their next voyage is to meet Grania, the female pirate, where they escape from a sea battle in a small boat; not without further attacks on Sean from the druid, whose name is Cathga. They have still not come to the right time to find old Peter. Back in their own time, they run into Cathga, who has with him a bully called Charlie Flanagan, who has constantly picked on Jik in the school playground. Cathga seizes Sean, tries to wrestle the dagger from him, and says that he will cut Sean’s throat with it, in retribution for its sacrilegious use. Nora manages to seize the dagger and escape with it. Then Sean’s uncle turns up, and Cathga disappears.

The final voyage is to a ship carrying emigrants from the Irish Famine. On this last trip, Colm comes with them, by mistake, together with his girlfriend, Bridie.

They finally meet a friend of old Peter, who gives them Peter’s lost notes on his invention. Cathga finds them, and tries again to seize the dagger, but Sean attempts to throw it overboard. The dagger sticks in the rail, but Jik pulls it out and manages to hurl it into the sea. Cathga, with a wail of despair, dives after it and disappears beneath the waves.

Taken back home by The Snapper, Colm admits to his children that only he himself can stop his drinking. However, Colm has learnt some things about himself, and so, too, have Jik and Nora. Nora has learnt that Bridie is not the monster she thought her. Sean has made two new friends, and given up his desire for revenge for his parents’ death. Colm is serious about stopping drinking. Best of all, Cathga is, they think, drowned, and won’t pursue Sean any more.