The guard (Kim Woo-bin) of an intergalactic jail must travel back in time to find the prisoners after realising they are now hidden across history. Unbeknownst to the host, these extraterrestrial prisoners are housed inside humans and pass away together with the host's physical demise. When a jailbreak goes horribly wrong in Korea in the year 380 AD, The Guard has his work cut out for him. Despite being a robot in human form, the Guard has several personalities. One of these personas saves a baby girl named Ean (Choi Yu-ri) from imminent death and returns her to the present. As she ages, Ean (now played by Kim Tae-ri) begins to remember robots and aliens, and she asks about the work of her "father."
In many ways, Alienoid is the best stuff in the best genre movies. Combining the action and CGI of a Marvel film with the wire work from Crouching Tiger, Hidden Dragon is undoubtedly a winning formula. The acting and directing all seem to be on the same tonal page, smoothly transitioning from epic to ridiculous on a whim. Another example is the blending of present and future technologies, such as the employment of weapons in Korea in the fourth century, which feels more natural than it should. The film contains numerous instances of Choi's bold strokes hitting and missing. A historical warrior squaring off against a man wearing a tom ford suit has a certain endearing quality.
Genre, tone, and story are all twisted in Alienoid to create an intriguing new world. The most of the sci-fi aspects of the plot look fairly nice, despite some choppy CGI. Because the plot drives the movie and Choi is having a blast both in front of and behind the camera, the dialogue never really needs to sing. Alienoid sets lofty goals and accomplishes virtually all of them.