From the introduction:
You are each playing a member of the Reality Restoration Unit, informally called 'riftwardens' or 'stitch patrol'. Your task is to walk into the gaping rifts in reality torn by the Haruspex, resolve the situation inside, and then get out.
To play Quantum Haruspex you need at least three players, but no more than five. Get some pencils, paper and a Tarot Deck. It is best to use a deck with an illustrated minor arcana with evocative imagery. Although the classic Rider Waite deck is a great pick, you may find it helpful to find a deck that is thematically close to the type of story you want to tell.