His expedition with two colleagues and his two children becomes an exploration of Ragnarok, the end of the world in Norse mythology - and the "no man's land" between Norway and Russia, where no one has set foot for ages.
Sigurd is an archaeologist studying the ancient Norse people known as the Vikings, continuing work that he and his wife had pursued together before her death five years earlier.
A meeting with funders in the Viking Ship Museum in Oslo intended to increase support for ambitious fieldwork that isn't well substantiated in Finnmark ends badly.
A breakthrough takes place when his co-worker Allan brings to him a stone tablet he found in Finnmark - the particular area in Northern Norway they've been focusing on.
After they retrieve the ship remnant from the museum, they're able to break the code enough to translate most of the runic symbols on it and interpret it as a map of an island in a lake which may hold extensive relics and/or treasure.
He decides to start his kids' (Ragnhild and Brage) summer vacation with them up in that area - doing on a smaller scale the work that they had been pursuing, with Allan and a small crew from the region.
As they continue and Sigurd and Allan attempt to retrace the ancient journey, Leif brings them to the only lake for miles around, which surrounds a small island - identified as the "Eye of Odin".
They discover mass graves - not only of ancient skeletons but also including a Russian soldier - and realize that the stone tablet was not in fact a map but a warning, written by Åsa, who refused to take part in her father's attempt to kill the still-living creature.
They find that the serpents are not exclusively water bound as they continue to attack the group, barely escaping back into the underground Russian bunker system.
[4] The website Twitch Film said: "It adds up to a fun family adventure, with Norwegian style and a welcome edge, something even Indiana Jones in his prime could never quite achieve".