The new season of Castle finds Rick (Nathan Fillion) rubbing elbows with daughter Alexis (Molly Quinn) after she joins his PI firm.

TV Line reports Alexis gets off to a rousing start that quickly has her solving more cases than even her vastly more experienced father. At the same time that they're engaging one another in a friendly game of one-upmanship, the two will also be seeking to find a way to incorporate new security specialist expert Hayley Vargas (Toks Olagundoye) into the equation.

Entitled "XY," the Season 8, Sept. 21 premiere also finds Det. Kate Beckett (Stana Katic) trying to adjust to her new promotion as captain, and Kevin Ryan (Seamus Dever) and Javier Esposito (Jon Huertas) "bumping heads" over the direction of their own careers.

According to TV Guide, while Hayley and Castle will be partners and closely working together, new show-runners Terence Paul Winter and Alexi Hawley insist the characters' relationship will not pose a threat to Castle's romance with Beckett.

"That was never our intention," Hawley said of the prospect of Hayley being a rival to Beckett for Castle's affections. "It's not going to happen."

The new season is also expected to feature the return of disgraced Sen. William Bracken (Jack Coleman), with his return being billed as "surprising."

Ann Cusack is also slated to join the cast over a two-part episode as Rita, with her character being described as someone with a "unique set of skills" and who has a "surprising connection to Castle."

The first two episodes of the new season are being billed as companion pieces "taking a very specific perspective on a series of important events" with the second episode entitled "XX."

"Castle" airs Mondays at 8 p.m. on ABC.