《Connection》A crime investigation thriller about a narcotics detective who was forced to take part in drugs, and the friendship between friends that deteriorated in order to track down the death of a high school classmate who left after leaving 5 billion in insurance money.

Zhang Zaijing is the ace of the anti-narcotics team of the Anhyeon Police Station. One day when he was busy dealing with drug dealers, his friend Park Zhunrui, whom he had not contacted for twenty years, suddenly came to his door...

Zhang Zaijing wanted to find out the truth that put him in trouble, but unexpectedly found that everything seemed to be related to Park Zhunrui...

After Zhun Rui's will was made public, everyone fell into chaos. Zhun Rui's wife agreed to conduct an autopsy. Jae Kyung and Yun Zhen were also determined to find out the cause of Zhun Rui's death.

Jae-kyung became suspicious of Chang-soo, and found a monitor in a mill near the death scene of Joon-seo. He thought he had found new clues, but...

In Beijing, he investigates the mill murder case alone, and infers from clues that it is related to the taxi driver. All the cases seem to have an invisible connection...

Jae-jin became suspicious after seeing Tae-jin. Although she suspected Chang-soo's involvement, Chang-soo responded fluently. Yun-jin further discovered their secret when she followed Ji-yeon...

Yunzhen breaks into the dean's office to interview Yuncong Hospital about a medication accident, while Jae-jing discovers that on the day of Zhunrui's death, an unexpected person was also present...

Jae-jing gradually pieced together the truth about Zhun Rui's death. After the three went to Xianyu, they learned the story of the medication negligence and found clues to the murderer of the Moulin Murder case...

In order to arrest the suspect in the Mo Mill Murder Case, Jae-kyung went to Zheng Yunhao's house; Yunzhen and Zhou Song came to Jae-kyung's house to discuss, but unexpectedly an uninvited guest came to his door...

Following the route in Beijing, Boss Yin's stronghold was found. Unexpectedly, Boss Yin was shot dead. In order to protect himself, Changxiu killed Boss Yin's men on the way to escort the prisoner...

After Boss Yoon was killed, the case fell into mystery again. In Beijing, he knew the location of Jung Yunho through Jiang Shizhen. Jung Yunho, who was being hunted, went to find someone...

The search network in Beijing gradually narrowed, and Jung Yun-ho lost control. Won Jong-soo, Park Tae-jin, and Oh Chi-hyun also suspected each other. When Jung Sangyi met Yun-jin in Beijing...

Jae-kyung, Yoon-jin and Zhou Song met with Kyu-min and Kyung-tai's mother and heard the ins and outs of the fire that year.On the other side, Tae Jin launched a counterattack against Chairman Won and Jong Soo...

Jae Kyung, Yun Jin and Zhou Song learned the truth about Jun Rui's death and discovered that the connections between friends were all for selfish desires. It was only after the tragedy that they began to reflect on the meaning of friendship.