"LUCA" (Last Universal Common Ancestor) is based on Charles Darwin's proposition that all species of life have descended over time from common ancestors.

Nam Shin is a son from a family who runs a large company. After an unexpected accident, he falls into a coma. His mother Oh Ro-Ra is an authority on brain science and artificial intelligence. She creates an android named Nam Shin III which looks like just like her son Nam Shin. The android pretends to be Nam Shin and he has a bodyguard So-Bong.

Life turns on a dime for a thriving prosecutor after meeting his new perky intern, who becomes a prime murder suspect soon after joining his office.