A year after Katla's eruption, the shattered survivors are still grappling with the aftermath. Suddenly, an ash-caked woman appears on the glacier.

Emerging from the shadows, a surprise visitor gets Gríma's full attention. As the ground beneath them shifts, Darri and Gunhild heed Katla's call.

The cold, cruel reality of life in Vík í Mýrdal comes home to Gríma. Darri studies his strange discovery in secret. Gunhild confronts the newcomer.

Is this a dream or a nightmare? Unsettled, Gríma returns to the camp for answers while Darri heads to Vík for a reunion. A torn Þór grows enthralled.

Face to face with an utter mystery, Gríma tries to understand her shadowy find. Rakel has a change of heart as Gísli deals with an unexpected arrival.

Sometimes shadows have minds of their own. At the scene of the accident, Rakel pours her heart out to Gríma. Darri canvases the crevasse for answers.

What's real, what isn't — and does it matter? The truth comes out, the fear grows and the mystery threatens to sweep away everything before it.