When a young woman goes missing near the sleepy Icelandic village of Vík, police inspector John Ward wants to cancel the Northern Lights Festival after his sole witness describes the kidnapper as a "Shadow". However, police commissioner Kári Ingason overrules him, fearing the loss of tourist revenue will cripple the village. Scientist Rakel Atladóttir and her peculiar assistant Rúnar offer to help Ward investigate the disappearance, plunging the trio into a fight for survival, with the fate of humanity in jeopardy against a malevolent cosmic horror