Anna and Will, were each other's first every-things: first kiss, first love, first and only relationship. Now, 10 years in, at her 30th birthday party, as he is about to propose, her brother Hale and his life partner Reece make a drunken toast, suggesting that they should sleep around before their inevitable marriage. The joke lands like a lead balloon, but the thought lingers until she proposes that they try opening their relationship--as a sexual experiment. Together, they venture out of the purely monogamous boundaries of their relationship and, along the way, evolve. Meanwhile, we also follow the relationship of the gay couple, Reece and Hale as they decide whether or not to become parents.