As high schoolers, Yoon Ha-Na, Yoon Ha-Ru, and Jung Woo-Jae were all close: Ha-Na and Ha-Ru as twin siblings, and Ha-Ru and Woo-Jae as judo competitors. As adults, Ha-Na becomes an actress with Woo-Jae serving as her bodyguard, while Ha-Ru becomes an internationally-ranked judo athlete. When a stalker kills Woo-Jae while he’s trying to protect Ha-Na, the twins are left heartbroken at their friend’s death. But after a car accident sweeps the twins out to sea, they wake up in 2010 – and in each other’s bodies. Ha-Ru and Ha-Na must now navigate their swapped identities, their shared desire to keep Woo-Jae alive, and the consequences of slipping back and forth in time - alongside Woo-Jae and Ha-Na’s developing feelings for each other.