The TV series is an adoption of the movie Limitless which was released back in 2011. The movie revolved around the concept of what happens when a person brain is utilized at is full potential.
The TV series takes the same concept. The main actor takes a drug called NZT and his brain starts functioning at its full potential. He remembers everything including his childhood memories. He helps the FBI to solve cases with his insights.
Bottom line
If u like the movie limitless, you will definitely like this series. and its getting better by every episode.