It co-stars Lee Joon-hyuk, Yoo Jae-myung, Shin Hye-sun, Yoon Se-ah, Jeon Hye-jin and Choi Moo-sung among a large cast of characters mostly belonging to the Ministry of Justice or South Korean police.

The series was a hit with both domestic and international viewers,[1] and received favorable reviews for its tight plot, gripping sequences and strong performances.

As they begin to unravel the mystery behind the murder, they find that their efforts are continually being obstructed by participants in a major corruption conspiracy between the Prosecutors' Office and a private chaebol (conglomerate).

[8] Unlike usual South Korean dramas, the series was developed as a potential multi-seasonal program, with most of the filming have already been pre-produced prior to its broadcast.

[12] For the second season, cast members Cho Seung-woo, Bae Doona, Lee Joon-hyuk and Yoon Se-ah, were all confirmed to reprise their roles.

[15][16] Ten songs were released from the soundtrack as singles in numbered parts from June to July 2017: "끝도없이 (Ad Infinitum)" by Richard Parkers, "먼지 (Dust)" Everlua, "소나기 (Downpour)" by Oohyo, "괴물처럼 (Monster Like)" by Tei, "웃어요 (Smile)" by Han Hee Jung & Sorae, the titular track "비밀의 숲 (Stranger)" by Yoon Do-hyun, "사랑할 것 처럼 (As if to Love)" by Kim Kookheon of Myteen, "물결 (A Billow)" by Yein of Lovelyz, "굿바이 잘가요 (Goodbye)"/"Back in Time" by Peter Han, and "묻는다 (Ask)" by Jung Won-bo of NeighBro & Jun Sang-geun.

[17] Of these, the songs "소나기 (Downpour)" and "사랑할 것 처럼 (As if to Love)" have managed to enter the South Korean Gaon BGM Music Chart at numbers 80 and 79, respectively.

The Korea Times reported that Bae Doona, who had previously appeared in the Netflix original series Sense8, proved to be crucial in the purchase of the drama.

[7] In her review for The Korea Times, columnist Park Jin-hai commended the writing as "finely intertwined", and wrote that audiences gave a strong response to this "drama for thinking people".