So ji-sub is returning to the small screen with upcoming MBC romantic comedy series “My Secret Terrius.”

The Wednesday-Thursday series that begins with a special two-hour pilot episode this week was filmed in part in Poland, and will feature a number of historic spots including Warsaw Old Town.

So, who has returned after 2 1/2 years’ hiatus, said during a showcase, “I’m a little nervous. I will watch from home tonight feeling nervous.”

“I chose the show because I thought it would be a fun show to watch as it features different elements such as comedy, romance and suspense,” he added.

So will play Kim Bon, a daytime babysitter who has a secret life as the legendary black ops agent from National Intelligence Service referred to as “Terrius.”

The show will see the unlikely duo with great chemistry of Kim, who lost his colleague and ex-girlfriend during a mission, and singer and mother Go Ae-rin, played by Jung In-sun, get to the bottom of a conspiracy.

So said he put great effort into the role, He went a diet, studied the character, changed his fashion style and took martial arts action classes for the action-packed comedy series.

Jung said she observed online communities for mothers to better study her character.

Despite the heavy storyline, director Park San-hun said the general tone of the show is upbeat and will shed light on a number of social issues including child care and married women whose careers are put on hold.

Park said the show will also put on display a day’s work for mothers, giving a unique comparison between a mother and spy in terms of how challenging each job is.

By Yim Hyun-su (hyunsu@heraldcorp.com)