'How to Get Away with Murder' season 3 updates, spoilers: Viola Davis promises 'big, unbelievable' mystery in upcoming installment

"How to Get Away with Murder" season 3 would be making an explosive comeback on television in September, and this early, its showrunner and lead star are teasing amazing things for ABC's legal drama.

Executive producer Pete Nowalk has earlier hinted that the third installment of the series would feature more dramatic storylines. Moreover, Parent Herald said this run would delve into the back stories of some of the characters. Michaela's (Aja Naomi King) adoptive family, as well as the identity of Laurel's (Karla Souza) dad, would be explored in season 3. Apparently, it's important to see how the people in both character's lives tie up to the kind of person they are at present.

"The storylines that I have in my head are very rich and complex, so I don't know when we'll tell them, but I think they are worth seeing," Nowalk said.

The arrival of "Dexter" star Luna Vélez as Annalise Keating's (Viola Davis) boss and new president of Middleton University would also present interesting challenges to the main protagonist. Apparently, while the character would be "self-assured, friendly, warm, and diplomatic," she would deal differently to those who hide secrets.

Speaking to E! Online, Davis said when "How to Get Away with Murder" goes back on air for its third season, "a mystery is going to be revealed in the first episode that is so big and so unbelievable I just think it's going to cost everyone something."

Those are ominous words coming from Davis, whose Annalise character seems to be always on top of a situation. The "Suicide Squad" actress also said she and her co-stars have been trying to figure out what this year's mystery is, but it looks like they're all stumped. Now if the stars of the series can't figure out season 3's mystery, it gives fans even more reasons to watch out for the show's comeback in September.

Meanwhile, TV Line reported that on Thursday night at the Television Critics Association (TCA) press tour, Nowalk confirmed that "NYPD Blue" alum Esai Morales and Amy Madigan, who once played a shrink on "Grey's Anatomy," have both been tapped for guest roles in the upcoming season of "How to Get Away with Murder." However, the showrunner has opted to keep their respective roles a secret for now.

"How to Get Away with Murder" season 3 is set to return on Thursday, Sept. 22 at 10 p.m. EST on ABC.