Happiness

Jung Yi-hyun investigates a murder where the victim has teeth marks on his neck. After surviving an attack, Yoon Sae-bom gets taken to a facility.

Sae-bom seeks Yi-hyun's help to realize her lifelong dream of homeownership. On move-in day, she meets her neighbors who seem overly cautious of her.

News breaks to the public of the disease that's been turning people rabid. Sae-bom heads upstairs to complain about the constant thudding noise.

The sudden lockdown puts Park Seo-yoon in Sae-bom's care. Yi-hyun investigates the fitness instructor's connection to Next.

A lack of supplies, phone and internet service further polarize the residents. Oh Joo-hyung offers to pay people to survey the area.

Joo-hyung visits the gym with a plan to get back at the couple in unit 501. Meanwhile, a person is let into the building while another heads out.

As a crisis breaks out, Han Tae-seok arrives offering help and good news. But he hides the real purpose behind his visit until he's alone with Sae-bom.

Sae-bom and Yi-hyun warn Oh Yeon-ok to stop picking fights with her neighbors. Yeon-ok seeks a way to turn everyone against the couple.

Residents grow suspicious of Sae-bom and plot to kick her out. Yi-hyun draws blood to prove Sae-bom's innocence and to sniff out the infected.

A neighbor's disappearance becomes a convenient coincidence for many of the residents. Yi-hyun makes arrangements to move his wife to safety.

Sae-bom and Yi-hyun head downstairs to turn on the emergency generator. Meanwhile, a cold-blooded killer awaits their return.

Realizing her feelings toward Yi-hyun, Sae-bom sets out to rescue her husband. Back at the apartment, the ugly fight for survival continues.