Callum scored The Sin Eater, an experimental theological drama set in post-Soviet Eastern Europe, influenced by German expressionism. The film follows the isolated protagonist, known as The Sin Eater, who takes on the sins of the recently deceased, only to find that the burden of his work is causing him immense suffering.

For the score, Callum incorporated experimental synthesis, blending organic sounds and manipulating them to reflect the character's emotional and spiritual torment. The unique sound design enhances the film's dark, atmospheric tone, amplifying its intense, surreal narrative.

The Sin Eater has been featured in numerous film festivals across the UK and Europe, gaining recognition for its innovative approach and compelling soundscape.