Once a season, Rookie Blue viewers know two basic things. One, Andy (Missy Peregrym) and Sam (Ben Bass) will question their relationship. Two, Oliver Shaw (Matt Gordon) will have a terrible, horrible, no good, very bad day.

Audiences saw the beginnings of what will be Shaw's awful day in last week's "Best Man" episode, when Andy and Sam informed him he was the main suspect in an internal investigation. By the episode's end, Shaw had walked away from the job in a state of calm rage. In this week's "Integrity Test" that bad day continues, as Oliver's team puts their careers on the line in order to prove their former boss' innocence.

In order to dig into the internal corruption and what exactly is in store, THR caught up with the man of the hour, Gordon, to get his take on the season's mole, getting comfy in a white shirt and how these events will effect the last few episodes in what could be the show's final season.

Was last week the first episode Oliver finally felt comfortable in the white shirt?

Two seasons ago when they put me into the white shirt I had a chat with [showrunner] Tassie Cameron because I was always very scared of it. Sometimes the white shirt means you’re not running around on the road and having adventures in the cruisers and stuff like that. So it was interesting Oliver to not like it and rebel against it.

In “Best Man,” as we move through the episode, Oliver maybe realizes that he can maybe bridge those two worlds; have the adventure and still feel connected to his cops. As the day plays out I think everything is all right … and then it isn’t.

Is there a bit of shoot-the-messenger that will carry forward into Thursday’s “Integrity Test”?

Things on Rookie Blue move pretty quickly. Your best friend in the world is your best friend in the world until something shifts or changes. We’re not like, 7-year-old little boys who have a little scuffle in the playground. But there’s nobody else for me to take it out on either. They gave me the latitude to get really angry at those guys. He’s slightly accusatory. That idea that you love me, Sam and Andy, you know me better than almost anybody. My home life is in shambles, I have Celery (Emily Hampshire), so that’s OK but it’s new and I have no history with her. Here are my two best friends in the world and it’s that idea that it’s almost a shock of, how dare you even bring it to me? The scene could have been super explosive but they were able to temper it by bringing in Chloe Rose as Izzy. She was there witnessing all of this, so that I have this person to ground me.

Is it not against Oliver’s nature to give up and quit?

There is so much history in six seasons of ups and downs and going to bat for your coworkers. There is so much in Oliver’s life that is not solid and when anybody does anything for that long, like 20 years, it’s as much a part of you as a person as it is just a job.

So to have that bomb … Oliver didn’t see it coming. And of course as soon as Sam and Andy tell him, then everything happens and he connects the dots. At that moment it’s 20 years of all heart, all in, and then it seems all for nothing. It’s just like, “Forget it, my kid is here, this is important, that thing is crushing and destroying so I’m out.” It’s a very human reaction. Of course he goes off with Izzy and becomes like a 50 year-old rock star.

Oliver has a bad day every season, but this coming episode is different in that he’s removed from the action. How do you play that?

It’s one of those things where it’s easy to give advice about what you should do with your day and how you can fix your problems, but it’s different when it comes and sits at your doorstep, when the problem is yours and yours alone. Maybe he just needed a break for a little while. Maybe he needed to sit alone, detached from that place and from his job, and just see what it’s like just to be Oliver.

Does he truly want to be alone?

It’s funny because they give him the space alone where he doesn’t know if he’s going back in the upcoming episode, but he goes straight to The Penny to have a drink. Which is like, all right … so he can’t do it on his own, he needs something familiar, and they sent him there. Perhaps he went there waiting, hoping that Sam will show up. I always suspected that perhaps he did.

What was interesting to work with is that it wasn’t his choice to leave. He made the choice to quit, but once they push you right to the edge of the cliff you either stand or get pushed. So he’s in completely uncertain territory. At the same time that he’s totally enraged with Sam, it’s like he wouldn’t want anybody else there.

Did anyone actually guess who the mole was?

I don’t think anybody knew. I remember having conversations after the table reads wondering and asking people, “Who do you think is?” They kept us guessing too, which is exciting.

You’ve had a lot of terrible, no good days. Do you have a series favorite?

The first one, when we met Izzy. Ari Millan, from Orphan Black and who is an amazing actor was in that. He’s a rock star. Missy and Ben (again!) had to come and talk me out of doing something stupid and shooting this 25-year-old kid who’s beating up my daughter. It was cool and special. David Wellington directed it and he did such a spectacular job. For me that stands out. I’ll remember that one forever.

The show still hasn’t been renewed for season six. Are you happy with where the series potentially ends?

If it goes again, great. We’ve been so tight and most of the people on the show are my great pals. While we’ve been talking Missy started texting me. If we go forward it will be just as incredible and if we don’t I think we’ve done something amazing.

Rookie Blue airs Thursdays at 10 p.m. on ABC. Are you waiting to see if the show has been renewed? Sound off in the comments below.

Twitter: @amber_dowling