'Elementary' Season 2 Spoilers: New Guest Star Exposes Joan's Past

Details of the second season of the CBS Sherlock Holmes drama “Elementary” are finally making their way out of the writers’ room. The one-hour drama, which follows Holmes (Johnny Lee Miller) as he solves cases with Dr. Joan Watson (Lucy Liu) in NYC, is set to return in late September in a special London-based episode.

Little has been revealed about the upcoming season, but new details have emerged that shed light into Joan’s mysterious past. As previously reported, Joan will use her and Sherlock’s trip to London to find out more about his checkered past but fans will also get a chance to uncover Joan’s decision to leave the medical world.

Executive producer Rob Doherty revealed to TVLine that “someone from [Joan’s] past” would be making an appearance early on in the season.

“We’ve alluded to a mistake she made when she was a surgeon that cost a patient his life,” Doherty told TVLine. “We’re going to meet someone, like a very real connection to that patient, and explore Joan’s feelings of guilt. At what point do you tap your guilt and give yourself permission to live?”

Actor Jeremy Jordan (of “Smash” fame) has nabbed the role of Joey Castoro, the son of Joan’s deceased patient. According to TVLine, Jordan’s character will make an appearance during an October episode and will test Joan’s “affections” for him “when he comes to her with an unexpected request.”

What sort of request could Joey possibly have for the surgeon-turned P.I?

Jordan won’t be the only one making a guest appearance in the detective drama. As previously reported, actor Rhys Ifans was tapped to play Sherlock’s brother Mycroft Holmes, who fans will meet in the season premiere. TVLine also reported that “True Blood” actress Lynn Collins was cast in a guest role as a “brilliant and beguiling math professor who helps Sherlock and Joan with the investigation of two murdered mathematicians.”

“Elementary” season two premieres on Thursday, September 26 at 10 p.m. on CBS.