Jang Dong-soo, Jang Dong-chul and Jang Dong-woo are three brothers who got separated at a young age after their parents died in an accident. They meet again twenty years later, but unaware of their blood ties, their ill-fated paths converge on casino territory where they find themselves at odds with each other.
Eldest brother Jang Dong-soo (Lee Beom-soo) followed in the footsteps of his father and became a detective. His greatest hope is to find his two brothers again and for the siblings to finally be reunited. Due to their different approaches to crime solving, Dong-soo clashes with Hwang Shin-hye (Oh Yeon-soo), a profiler who recently returned to Korea after studying overseas. They eventually gain a mutual respect for each other as colleagues, but find themselves in conflict once again when they learn that the gangster they're after is Dong-soo's own brother, Dong-chul.
Middle brother Jang Dong-chul (Kim Jae-joong) grew up as a petty thug on the streets, using his fists and wits to survive until he climbs to the top of a crime syndicate. Now a gang boss, he conceals his real identity and uses the name Heo Young-dal.
Youngest brother Jang Dong-woo (Im Si-wan) was adopted by a rich chaebol family, and now under the name Yoon Yang-ha, is being groomed as the heir to a casino empire. With no memory of his biological family and raised believing that the world revolves around money, Yang-ha is cynical and cold-hearted. Until he meets Oh Jung-hee (Baek Jin-hee), an poor girl supporting her family by working as a casino dealer, who changes the way Yang-ha sees the world. But he has a rival for her heart, Heo Young-dal.