Two deaths in a Leipzig apartment building leave The Quartet facing numerous mysteries. As tensions rise, everyone in the multi-unit dwelling becomes a suspect, mired in arguments, lies, and secrets. Antje Engel is discovered bludgeoned to death in the basement, while her neighbor Hannes Glöckl dies almost simultaneously from poisoning. It could be that these events are mere coincidences, or perhaps there is a sinister link between the two deaths.