Continuing from Episode 2, Sunwoo really managed to uncover Sera's secret.
Sera couldn't deny it anymore but she got back at Sunwoo's childish tricks by playing her own. She told him that a bird poop on his head, and then on his chest. When Sunwoo took a look and bowed his head, Sera then said, "You're great at showing respect."
She then went back to her room thinking how Sunwoo found out about her secret.
Later that day, we see Sera helping her bestfriend, Nahee, at the opening event of her bakery.
A while later Sera also approached Sunwoo to return the dress that she used. Sunwoo is still sulky so he didn't want to accept it. In the end, Sunwoo had no choice but to let Sera come with them as he still needs her for their investigation.
They went to the hospital, and there they confirmed that it was the hospital where Oh AhRa volunteered. To get more information, Sera ended up disguising as a patient as well as a newly wed couple together with Sunwoo.
Everyone believed their disguise but Nahee almost blew it when she rushed to the hospital thinking that Sera was really sick. To prevent her from making a scene, Jinmo even drank milk even though he's allergic to it.
That night, Sera and Sunwoo were forced to stay together as the other patients stopped Sunwoo from leaving saying that he should stay and take care of his wife.
Sunwoo made Sera sleep at the extra bed but the next morning, Sera had her revenge when the other patients saw what happened. She acted like her arms are hurting so she asked Sunwoo to feed him instead.
Back to their investigation. Our three detectives managed to pin-point the Nurse named Park Eunjeong as their suspect. When Sera and Sunwoo tried to confront her, she ran away which resulted to a wild chase inside the hospital.
Using her ability, Sera managed to follow Park Eunjeong. She almost got her but then, Park Eunjeong injected a drug on her which made her lose consciousness.
The same happened for Sunwoo that's why they woke up tied together inside the supply room.
Thankfully, Jinmo came to untie them and so they went on to follow Eunjeong using their GPS.
They found her and the episode ended with the three meeting not only Eunjeong but also Oh Ahra who turns out to be still alive.