In 2020, Han Tae-sul (Cho Seung-woo) was a genius engineer and tech magnate, the CEO of the Quantum & Time Corporation, which he ran together with his friends Eddy Kim (Tae In-ho) and Dr. Kim Seo-jin (Jung Hye-in). Kang Seo-hae (Park Shin-hye) was an elite soldier from the post-apocalytic 2035 sent back to the present to stop Tae-sul from inventing an innovative piece of time-traveling technology which would trigger a nuclear war on October 31, 2020, one that would wipe Korea off the map.

Though the corridors of time, Tae-sul and Seo-hye evaded threats from the Control Bureau under Mr. Hwang (Choi Jung-woo), the Asia Mart tech crew under Mr. Park (Sung Dong-il), and Han Tae-sul's arch nemesis since childhood, Seo Won-Ju, codenamed Sigma (Kim Byung-chul). Tae-sul got reunited with his elder brother Han Tae-san, whose death 10 years ago still made him feel guilty. Seo-hae got reunited with her beloved father (Kim Jong-tae) and late mother (Lee Yeon-Soo).

What was most remarkable about this series was its high-tech science fiction premise, not a common topic in K-dramas. It had ambitious scenes of major production value which they pulled off very well considering that this was TV. In Episode 1, Tae-sul was already trying to avert a commercial passenger airplane from imminent crashing. In Episode 9, there was a sequence of even more massive scale -- the destruction of Seoul by a continuous hail of nuclear warheads.

There were several elaborate action scenes to keep the adrenaline of the viewers pumping. In Episode 3, Tae-sul and Seo-hae outrun a horde of assassins in and around the Busan Convention Center. In Episode 4, there was an exhilarating scene of flying drones chasing a car as it navigated along narrow city streets. There would be plenty more such fight and chase scenes as the series went on, but for me, nothing really matched the complexity and excitement levels of those two.

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Park Shin-hye felt miscast as Seo-hae. She was generally so aloof and cold, uninteresting with little emotional connection to the very end. Her romantic chemistry with Tae-sul was also rather weak. Seo-hae's contemplative scenes by herself or those conversations she had with her father Kang Dong-ki (Kim Jong-tae), felt very repetitive. Even the subplots of characters connected to Seo-hae do not play out too well, like restaurant boy Choi Jae-Sun (Chae Jong-hyeop) who loved her, or new Control Bureau recruit Jung Hyun-gi (Go Yoon), who hated her.

It was the megalomaniacal Tae-sul vs. Sigma rivalry which was the most interesting storyline, especially as it became more fleshed out only in Episode 13. The backstory of Seo Won-ju was a deep hole of physical and mental abuse since childhood into young adulthood, which led him to become an evil mass terrorist, which Kim Byung-chul played with wicked glee. Han Tae-sul was an annoying, narcissistic, self-centered, billionaire tech genius but at least Cho Seung-woo still managed to give him a modicum of charm and heart.

It was not really too easy to get into the story at first with all the jargon used to describe the "uploading" and "downloading" of people, or the mechanics involved in such time travels. A plot-line about time-traveling, while interesting, can really result in several plot-holes when put under close scrutiny. Characters from the future went back to change events the past. There came a point when there were too many characters going back and forth in time, it eventually became difficult to follow all the little details in the flow of the story clearly.

Characters were allowed to co-exist with their younger selves in the same scene or even in one single location. They were not only there to observe (like in emotional Episode 11), but they were also able to actively intervene with the ongoing events (like in the finale Episode 16). It made for very good drama, even if they seemed against rules of quantum physics.

However, with such a broad futuristic palette at its disposal, this series promoted themes of guilt and regret, giving it a generally downcast mood, which may not be easy to binge.

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