Criminal Minds: Evolution Kicks Off Season 3 With a Killer Who Drowns in Darkness

Criminal Minds: Evolution is back, and it wasted no time diving into dark waters — literally. 

Criminal Minds Season 18 Episode 1 (or Criminal Minds: Evolution Season 3 Episode 1, who really knows anymore?), “Swimmer’s Calculus,” is a haunting, high-stakes season opener that plunges the BAU into the mind of a twisted killer who uses pools as a psychological battleground. 

But as chilling as the unsub’s tactics are, it’s the psychological fallout, ongoing Voit storyline, and Tyler Green’s evolution (pun intended) that make this episode sink its hooks in deep.

Let’s start with the obvious: seeing anything in the opening scenes is nearly impossible. Paramount+, I beg you to invest in a flashlight or two. The darkness is so thick it borders on parody. 

What we can discern involves a capped man slurping coffee and luring a stranger before spraying him in the face with aerosolized fentanyl. A cop arrives, gets tricked by a wasted brother ruse, and releases the perp. No ID check? No suspicion? Just vibes, I guess.

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Cut to a beach party that screams bad idea, where a woman wisely rebuffs a drunk dude who wants to follow her into the water. 

She’s got the instincts of a Final Girl, but alas, this isn’t that kind of show. When the guy stumbles on a corpse in the surf, the vibe shifts to full BAU mode.

As always, our team arrives with the speed of teleportation, ready to unravel the unsub’s twisted logic.

The killer has a pattern: puncturing victims’ ribs so they fill with salt water and sink. It’s a forensic misdirect that only works if bodies aren’t found — but a cold front changed the ocean’s currents, and voila, bodies are back on shore. 

Enter Tyler Green, now a full-fledged FBI trainee (yes!) and working hard to stay close to the team. Unfortunately, he hasn’t gotten his field office assignment yet. Spoiler alert: it’s not going to be D.C.

Tyler’s analysis reveals the latest body wasn’t actually an ocean drowning. Instead, swimmers calculus — brown residue from chlorine — points to a pool. 

The unsub is drowning people in his backyard and making it look like they died at sea. That revelation alone is enough to send chills, but what really drives the horror home is the method: forcing people to tread water until exhaustion claims them. 

He watches, he waits, and he lets them die slowly. It’s more than sadistic — it’s deliberate psychological torture.

And that’s where the show excels: in peeling back the layers of criminal psychology. Why do people like this exist? Why do they want others to suffer as they did? 

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Franklin, the killer, witnessed his family drown under a pool tarp when he was ten. His alcoholic lifeguard father forced him to repeat swim tests he couldn’t pass. 

The trauma didn’t just stay with him — he made it his identity. But here’s what always gets me: what makes someone leap from pain to replication? What turns trauma into a weapon?

This show has never been about easy answers, and that’s what makes it worth watching. 

JJ and Tara’s speculation about aquaphobia and Tyler’s input about the killer revisiting his own trauma are the kinds of threads that elevate this beyond case-of-the-week storytelling. It’s about how fear curdles into hatred, and how the mind builds its own prison.

Meanwhile, Rossi is having his own psychological crisis. With Voit in a coma after being shanked in prison (and then somehow managing to kill his attackers before collapsing), Rossi is under the microscope. 

OPR thinks he might be involved. And while he insists he had nothing to do with it, he also has that Rossi grit: “If I wanted him dead, he’d be dead.” God, I love him.

Voit’s brain scans are baffling — he’s got damage in the prefrontal and occipital lobes, but also decades-old scarring. As Prentiss quips, his brain resembles that of a retired linebacker. (Ouch, and honestly, same. My brain might have similar mileage.) 

Penelope, ever the empath, sees something different. She believes there’s an ember of humanity left in him. Luke doesn’t agree, but he believes that she believes. That’s enough for now.

The episode’s most harrowing sequence involves a mother and daughter forced into a pool after their husband/father is executed for refusing. 

They must tread water beneath a covered pool while the killer watches from above, inhaler in hand. It’s terrifying. 

The mother coaches her daughter to conserve energy, and eventually, they use a corkscrew (a birthday gift) to poke a hole in the tarp to survive. It’s equal parts horror and heroism.

Tyler doesn’t swoop in to stab the killer, but the knife he carries as he awaits the OK to carry a gun comes in handy. He stabs the pool cover, tearing through it to free the women and get them air. 

That moment of rescue is tense and triumphant, and required after Franklin crushed the pool cover remote under his boot and shot himself in the head. 

His last words, something along the lines of “maybe this was always the plan,” are haunting. Did he want rescuers to feel as powerless as he once did? Was the whole thing a meticulously staged recreation of his own trauma?

Frankly, I’ll never understand the criminal desire to torture others as you have been tortured. How is their brain wired that they think this will heal them in some way? Have there been studies? It’s nuts.

Tyler’s reward? A field assignment in Mobile, Alabama. It’s not what he hoped for, but if you think he’s staying away from the BAU for long, you haven’t been paying attention. This is his origin story, and I’m here for it. 

Still, it begs the question: how might Tyler find his way back to Quantico? His inside knowledge of Voit, his potential as an analyst-turned-agent, and his proven instincts in the field might work in his favor. 

Add in the fact that Rossi is under scrutiny with OPR breathing down his neck or the possibility that the team might soon face emotional upheaval they didn’t plan for and suddenly, having someone like Tyler close feels less like a luxury and more like a necessity — even if the FBI isn’t ready to admit it yet.

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Rossi, too, has a small win. He discovers Voit had stashed a shank in the laundry room — a detail that clears some suspicion but doesn’t fully exonerate him. Still, it’s momentum.

Emily points out that Franklin’s comment, that this was all part of the plan, helped them uncover another clue: Franklin had been uploading torture videos using encrypted codecs. 

It’s eerily similar to the methods Voit and his network once used. And let’s be honest, there’s no way Voit’s network just disbanded because he’s in a coma. 

These guys aren’t influencers who log off when things get rough — they’re darkness junkies. Torture and death are their brand. That chilling breadcrumb is almost certainly the throughline for the season ahead, and it means one thing: Voit isn’t going anywhere.

And just when you think the episode is over, it hits you with a brutal closing shot. 

Voit, the puppy-eyed coma patient Penelope has been sitting with, suddenly wakes and begins strangling a nurse. No alarms, no monitors. Just pure, calculated violence. Whatever he is, he’s back. But seriously. Would any of you have gone into that room with one of his arms unrestrained??

Welcome to Criminal Minds Season 18. It’s going to be a ride.

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