Coming from two different backgrounds, Gong Ryong and Eve Kim embark on a space mission. But trouble strikes after launch, jeopardizing their expedition.

Upon arriving in space, Ryong panics as Eve threatens to ruin his secret mission. Shortly after, a crisis emerges, forcing Ryong to attempt a novel feat.

Determined to carry out the secret mission himself, Ryong tries to circumvent Kang Kang-su. During a space walk, Eve experiences a sudden problem.

With Eve's life in jeopardy, Ryong watches helplessly — as protocol prevents him from saving her. With every passing second, she loses precious oxygen.

Following Ryong's sudden confession, Eve discovers a hurtful truth unfolding back on Earth. Soon, she learns of an even more disturbing reality in space.

Eve discovers an unethical secret, forcing her to act decisively despite Ryong's objection — which drives him to take matters into his own hands.

After Ryong learns the results of his experiment, a potential calamity approaches the crew — threatening his safety and the survival of his work.

Eve risks everything to heroically rescue Ryong, facing treacherous danger. However, returning home seems increasingly improbable.

With Ryong and Eve stranded in space, those on Earth scramble to save them — albeit for different reasons. Park Dong-a steps forward to take the risk.

Despite their promises in space, Ryong and Eve return to earthly realities — facing duty, recovery, suspicions, confessions and lingering longing.

While Ryong and Eve adjust to normal life, Chief Kang requests a detailed report of their time in space — leading them to agonize over their story.

Choi Go-eun confronts Eve after encountering her at Ryong's place. Chief Kang advises Eve not to see Ryong again — despite Eve's true desires.

Chief Kang summons Ryong and Kang Kang-su regarding their forbidden experiment in space. Eve uncovers a painful truth about her past.

A deployed investigative team discovers Ryong's cell phone in space — sparking an inquiry into who is responsible for the unauthorized events there.

The consequences of the experiment in space finally manifest, leaving Ryong devastated. Later, Eve learns that her life is about to change forever.

As Eve's new state prevents her from coming back to Earth, Ryong commits to joining her in space. Once there, they debate a risky return to Earth.