The series is set in Ocean Beach, San Diego and focuses on ex-cop and recovering alcoholic Hank Dolworth (Donal Logue) and his best friend, former criminal Britt Pollack (Michael Raymond-James), who both decide to open an unlicensed private investigation business.
According to Nielsen Media Research, the episode was seen by an estimated 0.725 million household viewers and gained a 0.4/1 ratings share among adults aged 18–49.
Hank is asked to interrogate Britt (Michael Raymond-James), then a thief stopped near the scene of a rape by Billy Whitman (Chris William Martin), the son of a powerful La Jolla family.
Later, Mark interrogates a drunk Hank, informing him Whitman was run off the road and evidence implicating him in the rapes was found planted in his trunk.
Laura’s reporting and their own recollections of the case show that he was involved in the rapes and planted the evidence in Whitman’s car, as he was the first officer on scene and made the victim recount the events to him in detail.
Club gave the episode a "B+" grade and wrote, "As always though, my complaints are more nitpicky than anything: minor gripes at a show that's capable of taking even an alcoholic stupor and finding its finer shading, as 'Sins Of The Past' does elsewhere.
"[3] Alan Sepinwall of HitFix wrote, "Though Terriers isn't exactly a show with a complicated mythology like Angel or Firefly, there is a lot of messy history to these characters that predates the events of the pilot.
It took the oldest trick in the TV handbook — a flashback episode that showed us how our heroes arrived at the point in their lives we're now following — and made it triumphant storytelling.
"[5] Matt Richenthal of TV Fanatic gave the episode a 4.7 star rating out of 5 and wrote, "Many shows make the mistake of using flashbacks as nothing but a gimmick, revealing very little about characters and simply assuming viewers will be happy with the mere idea of going back in time.
"[6] Cory Barker of TV Overmind wrote, "'Sins of the Past' is a flashback episode to the case that cost Hank his job and his marriage and it's also unbelievably powerful.