Jon (Domhnall Gleeson) is a young man with a dream: He wants to be in a band. He wanders the streets looking for something, anything, to give him some inspiration to write a song, and spends endless hours twinkling at his keyboard. Yet everything he pens is absolute crap and he seems much better at writing tweets than lyrics.

When Jon gets a sudden offer to fill in for a keyboard player in a cult band from out of town, he jumps at the chance. There he meets Frank (Michael Fassbender), the band¡¯s eccentric singer ¡ª best described as ¡°random,¡± in the parlance of our times ¡ª who not only performs wearing an oversized papier-mache puppet head, but wears it 24/7 and never breaks character.

Frank is at once childlike, bizarre and on the edge, but more important to Jon, it seems, is that he¡¯s a gigging musician. When Frank¡¯s manager (Scoot McNairy) asks Jon to join Frank¡¯s band (Maggie Gyllenhaal, Carla Azar and Francois Civil) for a recording session in a remote Irish cottage, he jumps at the chance, though he¡¯s shocked when he arrives to find rationed food and a cultlike process of deconditioning.