After Jack becomes apprenticed to a Druid bard, he and his little sister Lucy are captured by Viking Berserkers and taken to the home of King Ivar the Boneless and his half-troll queen, leading Jack to undertake a vital quest to Jotunheim, home of the trolls. Gathering the lambs -- Apprentice -- Shadow across the water -- Valley of lunatics -- Hrothgar's golden hall -- Wolf-headed men -- End of days -- Rune of protection -- Rider on the nightmare...

Thirteen-year-old Bree asks God for protection when she and her brother Devin are captured and taken from their home on the Irish coast by Viking raiders in the late tenth century.

Briana O'Toole arrives in Norway to face her new life as a slave, all the while praying that God will send her brother, still in Ireland, to buy her freedom.

Thanks to their magical book, Fred, Sam, and Joe inadvertently travel through time to to 1000 A.D. where they sail with Leif Erikson, attempt to escape from his evil cousin, and try to find a way back to their own time.

In tenth-century Norway, Bree and her friend Lil, buoyed by their Christian faith, have escaped the Viking ship but are pursued by Mikkel; while in Ireland, Devin's anger about his sister's kidnapping prevents him from forgiving her captors.

Hiccup, stranded with Toothless on the Beach of the Broken Heart and being hunted by an old enemy, faces Ug the Uglithug, Berserks, and Scarers and tries to save Fishlegs from the Beast.

Raised to be a warrior, seventeen-year-old Eelyn fights alongside her Aska clansmen in an ancient rivalry against the Riki clan, but when faced with her brother's betrayal, and driven by a growing love for her brother's friend Fiske, she attempts to unite the two clans.

Their magic tree house takes Jack and Annie back to a monastery in medieval Ireland, where they try to retrieve a lost book while being menaced by Viking raiders.

Two years after their adventures in The Land of the Silver Apples, the apprentice bard Jack and his Viking companion Thorgil confront the malevolent spirit of a vengeful mermaid and begin a quest that casts them among the fin folk of Notland.