The Season 1 finale of A Million Little Things revealed that Jon's (Ron Livingston) depression kicked into high gear after his best friend was killed on the 9/11 flight from Boston that was diverted into the World Trade Center. That best friend left behind a pregnant fiancee — Barbara Morgan (Drea de Matteo) — who quickly remarried in order to give her newborn child a father. Jon angrily abandoned Barbara, and her newborn, when he learned of her new relationship and the guilt of that rage contributed to his suicide years later. Barbara's child is now a big teenager named PJ (Chandler Riggs), and he's going to shake things up for Jon's family and the friends he left behind when he committed suicide in the first season.

"PJ knows a lot more than he's leading on with," Riggs told TV Guide during a visit to the A Million Little Things set earlier this month. "There's a lot more than he knows that he's not saying that will be revealed later in the episodes."

PJ introduced himself to Rome (Romany Malco) at the end of Season 1 after finding Rome's script in the hospital waiting room. The two struck up a quick friendship and bonded over their own struggles with depression — but that meeting may not have been by chance, after all, especially after PJ discovered the video of Jon revealing that PJ might not truly be his adopted father's child. Rome is a good way for PJ to get the answers he needs about Jon's message and what it truly means.

"PJ definitely has an agenda of his own and he's definitely playing up the...mentor-mentee [relationship]. Rome will be brokenhearted [when he finds out]," Malco teased. However, there is hope that both Rome and PJ can both get what they need out of the relationship, even with the broken trust.

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"Rome is a genuine guy. If there's anything in PJ's narrative that could lead to more truth...there's no way you could turn Rome into a guy that would cut that off," Malco continued. "Even when it's the most painful, Rome is always on a quest for truth. If PJ presents something believable, whether it's true or not, Rome is going to want to know."

Riggs, of course, is the first to defend his character and whatever duplicitous actions he will take in Season 2 to discover the truth about where he came from, and Jon's part in all of it.

"He's a very justified character. Everything he does, he has a pretty good reason for — at least from my point of view," Riggs said. "The thing that I love most about PJ is that everything he's going through, all of the unanswered questions, his reconciliation after each revelation, it's all extremely realistic."

Is the rest of the gang going to think so when they find out why PJ is really hanging around though? That remains to be seen.

A Million Little Things premieres Thursday, Sept. 26 at 9/8c on ABC.