"Castle" returns with Season 8, Episode 2, "What Lies Beneath," and series star Nathan Fillion finds himself consumed with finding the killer of a reclusive author who also happens to be his idol.

Spoiler TV reports as he and Captain Kate Beckett (Stana Katic) delve into all the bloody details, they soon realize everything isn't exactly as it seems.

The same thing can be said of Beckett's mysterious disappearance following an unexplained phone call from Vikram Singh (Sunkrish Bala), an analyst in the same attorney general's office where she once worked.

In time, it's also hinted that Beckett's old nemesis Senator William Bracken (Jack Coleman) may be the one behind it all. A recently released promotional trailer shows her visiting Bracken in prison and him warning the new captain that she is overstepping her bounds.

All this plays out while Castle shares with daughter Alexis (Molly Quinn) that he's not sure he can ever completely trust her again given the way she has consistently kept secrets from him.

Yet another promotional video shows Castle confronting Beckett over all her deception, prompting her to insist to him it was all done for his protection. In time, she also remains him of the anguish he put her through when he previously went missing for several weeks.

"Castle" also stars Jon Huertas as Javier Esposito, Seamus Dever as Kevin Ryan, Tamala Jones at Lanie Parish. This season new co-showrunners Terence Paul Winter and Alexi Hawley have added Toks Olagundoye in the role of security expert Hayley Vargas.

Previously there was speculation Vargas might challenge Castle and Beckett's relationship and eventually emerge as a love interest for Castle. But show execs have quickly shot down the rumors.

"Castle" airs Monday night on ABC at 8 p.m. ET.