Mouse (Samuel Hunt) will become increasingly adamant to re-enlist in the army come "Chicago P.D." season 4 episode 5, titled "A War Zone."

This means that it will be extra challenging for Halstead (Jesse Lee Soffer) to convince his best pal to do otherwise as it appears that Mouse is close to making up his mind.

The synopsis for "Chicago P.D." season 4 episode 5 teases that Mouse is, without a doubt, serious about returning to the army. This would mean that he could be out of the team.

His exit will be another blow to the intelligence unit as Detective Antonio Dawson (Jon Seda) is also set to leave, with Seda tapped as series regular for "Chicago Justice."

Seda is still very much part of "Chicago P.D." season 4, and fans will see him a lot in upcoming episodes, but his days on the show are numbered.

It is believed that Dawson's departure would allow Mouse to officially be part of the team. It is not looking like this is possible come "Chicago P.D." season 4 episode 5, though, as he is certain about his next move.

As teased before by executive producer Matt Olmstead, Mouse's decision will allow fans to see how deep and strong his friendship with Halstead is.

"Halstead is adamant about him not going back over. Which has much more to do about Halstead than Mouse," Olmstead told TV Guide.

"It culminates in a really moving story about that relationship, that friendship between Halstead and Mouse, the loyalty, the promise that they would look after each other over here," he went on to say.

Mouse is expected to have a change of heart at some point, although that is not for certain yet. Fans will have to tune in to "Chicago P.D." season 4 episode 5 to find out.

The installment will also see the team deal with the city's "most notorious crime lord," who the team has been after for a decade and a half.

"Chicago P.D." season 4 episode 5 will air on Wednesday, Oct. 26, at 10 p.m. ET on NBC.