Detective Carter travels through time to work with Detective Riley on a cold case. Well, not really.

***SPOILER ALERT****

The show starts with a flashback to the beginning of season two, and a stakeout with Carter and Reese. Her banter with Reese fighting over the radio makes you realize how much Carter is missed. Flash to the present, and Reese catches a murder case that leads him to an old case Carter was investigating. Team Machine is split up with Reese on his own and Finch working a number with Root and Fusco. To be honest, and ironic the Number this week was truly irrelevant to the story. The case was just there to keep Finch and company busy while Reese went off by himself, on an adventure of self-discovery.

The tragedy that took Carter away last season seems to still weigh on Reese, and affects his decision-making as he investigates Carter’s old case. He tells no one what he’s doing or where he’s going, so he can have this last bit of Carter to himself. That ends up biting him in the ass, but we’ll get to that later.

The writing is really impressive this go round as they weave flashbacks of Carter tracking a murder case, and Reese following her footsteps in the present. Amid all of that, the flashbacks with Reese and Carter hanging out during a stakeout play counterpoint. The stakeout is especially interesting since Reese and Carter share stories that have never been seen on screen. At this point Reese pulls out an old photo of his long lost love, Jessica to show to Carter, and that is the first red flag on the play. The photo he pulls out is the very same one he pulled out of Carter’s cold case box in the present. What? This is where the show goes off the rails, but in a good way. The whole flashback stakeout scenario is not real, but the effects of hypothermia. Reese has been shot, and is freezing to death in a stalled out car.

Once this fact is revealed the writers take it to another level, and mix Reese’s confusion and disorientation into time jumps. Carter is serving as his survival instinct, pushing him to do what is necessary to make it through the freezing temperatures. She is also serving double duty by pointing out that he could have expected help if he wasn’t so closed off, even from his friends. Reese has to delve deep to realize where his isolationist personality began, which lead him to break up with Jessica in the first place.  Every dead soldier he knew, including the enemy, had a picture they carried with them.  Reese figured if he had no one at home he cared about then he could concentrate on being alive.  Flawed theory since that meant he wasn’t fighting for anyone either.  The most heart-breaking element of the entire trial is Reese firmly believing he shared his story of Jessica with Carter. She reminds him that whenever she tried to share something personal (not just weather and sports), he would make a joke or change the subject. It never happened, except in his mind. Now it’s too late.

What is spectacular about Carter, and more recently Shaw, leaving the team is that the tension of Reese bleeding out and freezing carries more urgency. Reese could really die. Alone, on the side of the road. It would be absolutely tragic, but instead he learns that he should let people close to him in, before they are gone. That revelation is building toward his budding relationship with Iris, but his relationship with Carter feels more poignant.

In the end, we assume Reese pulls through when headlights from an oncoming car approaches. Carter, who had been holding his hand as he drifted off, disappears. Was she just a fevered hallucination brought on by hypothermia or is Carter watching over him? You decide.

Check in for the last new episodes of the season when the war between the intelligent machines finally comes to a head.

Person of Interest airs on Tuesday at 10/9c. Watch full episodes on CBS.com, Hulu Plus, Amazon Instant Video and On Demand (check with your local cable provider).