'NCIS' season 14 episode 5 spoilers: Quinn lets Gibbs in on a secret

Alex Quinn (Jennifer Esposito) has shied away from doing field work despite her skills, and fans will learn why in the next episode of "NCIS" season 14.

Quinn has the exceptional expertise and knowledge that Agent Gibbs (Mark Harmon) believes will make her an appropriate replacement for Tony Dinozzo (Michael Weatherly).

However, as revealed in "NCIS" season 14, Quinn decided to stick with being an instructor at the Federal Law Enforcement Training Centers (FLETC), where Gibbs finds her when she first persuades her to return.

But there is a reason she will not want to be back in action and it will be revealed in "NCIS" season 14 episode 5 titled "Philly."

The promo for an episode teases that she lost someone dear to her while she was out on the field for a case. The tragedy appears to have affected Quinn so much that she stayed away from the dangerous job completely.

Like fans, Gibbs will also learn about Quinn's tragic past in "NCIS" season 14 episode 5 as he sends her in Philadelphia with Bishop (Emily Wickersham) to investigate the case of a missing M16 officer who is linked to the death of a petty officer.

At one point in the promo, Quinn confronts Gibbs. "You don't know anything until you walk in my shoes," he tells her as tears rolled from her eyes.

Meanwhile, "NCIS" season 14 episode 5 will finally see Duane Henry (Clayton Reeves) return for the first time this season. It is only right to have him back since MI6 is involved in the case being investigated.

Lastly, the promo for the episode also teases more of Nick Torres (Wilmer Valderrama) and his fun and cheeky tactics in getting information. His bit will certainly balance out the emotions in this installment.

"NCIS" season 14 episode 5 "Philly" airs on Tuesday, Oct. 18 at 8 p.m. EDT on CBS.