Cassette is a documentary mixtape about a musical format that refuses to die. As recorded music continues to move away from the tangible artifact, a strange romance now surrounds the cassette, with rising sales over the past decade to prove it. Far removed from this resurgence is the format’s inventor Lou Ottens. Now 91, Lou lives out a secluded retirement in Holland, where he is happy to leave the audiocassette in the past. A stubborn progressive, Ottens struggles to understand why a new generation is turning to tapes to spread their music. Through a series of one-on-one interviews, Lou confronts 50 years of mixed emotions about his creation. Influential musicians like Henry Rollins, Ian MacKaye, and Thurston Moore add personal stories to the narrative, while indie labels like Burger Records introduce the cassette to a new generation. These colorful vignettes play out like a mixtape, made to remind Lou Ottens of the importance of his invention.