Addicted tells the story of a married couple Eun-su and Ho-jin, whose younger brother Dae-jin also lives with the inseparable pair. Seemingly they enjoy the perfect life in harmony, Ho-jin is a caring, loving husband, while Eun-su shares the same uncontrollable affection. They are the perfect twoseome, whose relationship is looked upon as solid and ideal, a yardstick, if you will, for others to measure up to, an unshakeable bond.

Dae-jin, meanwhile, is carefree, behaves erratically and could do with finding himself a decent relationship in which he would have to care for someone else other than himself. However, their tranquil world comes crashing down around them when tragedy strikes one fateful day when two separate car accidents put both brothers in a coma. Dae-jin crashes his car during a car race and Ho-jin is involved in a taxi collision while on his way to the racing circuit. Only the younger sibling wakes, leaving Eun-su to restart her life alone without her husband.

Left disorientated, events take a strange twist as Dae-jin’s behavior changes, beginning to resemble that of Ho-jin, leaving everyone familiar with his antics questioning his peculiar mannerisms. Through the trauma and hysteria, Dae-jin believes he is in fact his brother and that he is possessed. Eun-su is left to wonder if her husband’s soul is trapped in the body of her brother-in-law or if he’s just mentally unstable.