Mr. Plankton

Hae Jo sets out to find his sperm donor, the biological father he never knew. He crashes Jo Jae-mi's wedding and drags her along.

Hae Jo recounts his first meeting with Jae-mi. While a huge fight breaks out at the sundae shop, Eo Heung and Wang Chil-seong's gang close in.

Jae-mi makes a tough choice between Hae Jo and her devoted fiancé. Soon they head down to Busan, while a mysterious figure arrives to bail Heung out.

Hae Jo spends meaningful time with Ko Jae-geun up in the mountains. Back in Seoul, Chil-seong corners Kkari and forces him to track down his old partner.

Heung reflects on his relationship with Jae-mi. After Hae Jo steals a boat to escape Chil-seong, they end up stranded on a deserted island.

Shaken by the island ordeal, Hae Jo slips into a slump his friend Yang Bong-suk can't lift. Meanwhile, Heung does everything to stay by Jae-mi's side.

Afraid of hurting Jae-mi again, Hae Jo tries to push her away. Later, he takes on a new errand and meets a young girl looking for her long-lost brother.

After learning about Hae Jo's severe condition, Jae-mi is determined to help him find his biological father. But when she returns, he's gone.

Now alone with Heung, Hae Jo reflects on his unfortunate life. After a tense reunion at Kkari's workplace, Hae Jo decides to confront his painful past.