Once upon a time there were four spirits that inhabited the same world, but in different planes. They co-existed, but could never interact. Until one day came the Fifth, who existed in all planes, and helped them live together, even separated.
But one day The Fifth was stolen away by a dark entity. Now the four must somehow make their way to where The Fifth is held captive and, with you as their guide, rescue the Fifth and live happily once again.
Quartet is a single player co-op puzzler where you must take control of four independent characters that don't interact directly, but must cooperate to reach a common goal.