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.

A shocking revelation that would ordinarily offer closure instead opens up a chasm of questions. History repeats itself as a deadly ash storm gathers.

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.

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.