The premise goes thusly: In the 13th century, at the onset of the Black Plague, a young monk named Morgan Pym (Chris Kramer) is tricked by the Devil into selling his soul to him, in exchange for not going to hell after the 10 year contract has expired, Morgan is tasked with collecting the souls of other people who dealt with the Devil after their 10 years of enjoying the outcome of the deal are up, and is effectively immortal.
However, at the beginning of the new millennium, after meeting with a junkie named Maya (Carly Pope/Sonya Salomaa) and nursing her back to health, he rediscovers his desire to help people and manages to persuade the Devil to allow him a 48 hour window to help find redemption for the people who dealt before their time is up and their souls are sent to hell.
Unfortunately not only is the Devil constantly throwing curveballs in Morgan's direction to distract him and impede his progress in saving souls, but intrepid journalist Jeri Slate (Ellen Dubin) begins to suspect Morgan of being trouble due to him being in the vicinity of several high-profile deaths (from his job as a collector) and serves as a constant annoyance and an impediment to his progress, all the while her autistic son Gabriel (Aidan Drummond) has an unexplained connection to the Devil, Morgan and the people he's trying to save.
If the show seems very formulaic to you, Morgan has 48 hours to save someone before they go to hell, many episodes do something to shake up the formula, the most common method being Morgan failing to save the person from going to hell, as such the show never loses its tension due to a 100% success rating on the part of the main character. Also the running B plot of Maya trying to stay sober and the C plot of Jeri trying to figure out who Morgan is while struggling to care for Gabriel, may seem out of place in a show like this but are always amazingly written and performed by the cast and never feel like they don't belong given the dramatic and mature nature of the series.
And speaking of which, this is not an action series like Buffy or Angel or Supernatural, there are no monsters of the week and Morgan rarely fights something and every time he does we know he won't die since so long as he continues to be a collector (even if he's actively sabotaging his job), he's completely immortal and heals almost immediately from any wound. This is a drama, and the climax usually involves people talking rather than people fighting (even though sometimes fighting happens anyway). If this sounds boring to you then I don't recommend but if you would like your genre TV with more drama and less action then the Collector is the show for you. Just keep in mind that it was canceled before all of its story arcs were resolved so you won't be (crushingly) disappointed once its over and it's really the only thing stopping me from giving it a 10.
The show is only available in its entirety on Amazon Prime, as the third season never got a proper home video release, so if you don't have an Amazon Prime subscription yet, this show (and The Man in the High Castle as well) makes it worth it on its own.