All four of them have been in a relationship before. Taeyeon with Leeteuk, Tiffany with Donghae. Both relationships failed. It's been 2 years, all still harbour feelings for their lost half, and never tried to find another. Only then, that they realise that what's lost cannot be recovered and decide to move on in life. There is a turnpoint. They fatefully meet at a dancing class. Taeyeon and Tiffany have already given up and have no thoughts of restarting their relationship. However, Leeteu