Whitney and Will are a perfect couple by all appearances, their relationship rock-solid, and their engagement soon to be announced. Before their impending nuptials, however, Whitney suggests a lighthearted experiment: why not give each other three romantic "free passes" before getting married? Three opportunities to imagine other lives before returning with new appreciation for each other. On what's meant to be the last night of a romantic Barcelona vacation, they agree to regale one another with details of these harmless trysts. They grin and bear it, and fall asleep feeling mostly satisfied, and relieved to be firmly together again.

But then a volcano erupts overnight, spewing a cloud of ash across Europe and grounding all flights indefinitely. Trapped in Barcelona, their paths intertwine with a star basketball player, his future dashed by a crippling injury, and a foreign exchange student with a double life, about to return home and face reality.

Whitney and Will flirt, provoke, dance, and drink. Over the next three days, they will use and be used by their new friends, once again testing the boundaries of their relationship-but this time, can it survive?