A body of a woman is found in the woods who is later identified as Mali Pryce, a troubled girl who went missing in 2011.
Leading actress Sian Reese-Williams commented that the series was more of a "personal drama" than a crime series, because of the multiple human stories involved, including those of the victims, the families of the victims, and the criminal protagonist.
In January 2021, the BBC announced that a third series had been commissioned to air later in the year, with Sian Reese-Williams and Siôn Alun Davies returning in their roles of, respectively, DCI Cadi John and DS Owen Vaughan.
The Guardian compared Hidden favourably to the Swedish Scandi-noir drama The Bridge, describing it as one of the "current powerhouse run of Wales-set dramas", with "scenes in Welsh to provide that sweet Nordic subtitles hit".
As well as a gorgeously gothic credits sequence, it features handsomely brooding landscapes, offbeat interior locations that go far beyond the usual bland corridors/offices of cop drama, and an ominous, skin-prickling soundtrack skilfully employed to heighten the sense of dread.