How Star Trek: Discovery Season 3 Episode 4 Will Change The Series Forever

One of the most intriguing alien races in the pantheon of Star Trek is the Trill. First appearing in the Star Trek: The Next Generation episode, "The Host," the Trill are essentially two races: a spotted, humanoid species and a clan of longevous, telepathic slugs.

The two races from Trill have a symbiotic relationship with the slugs taking up residence in compatible, humanoid host bodies in a process called "joining." Once the host and symbiont are joined, they form a new consciousness and personality which represents the memories of both individual entities.

If all of that sounds complicated, don't worry — we're going to explain the ins and outs of how Trill culture and physiology work shortly. First we have to acknowledge why we're talking about the Trill right now. In the season 3 episode of Star Trek: Discovery "Forget Me Not," we're introduced to something remarkable for the first time — Adira (Blu del Barrio), a human in the process of becoming long-term host to a Trill symbiont. Prior to this episode, that was considered a giant no-no.

Not only does Adira have a symbiont inside them, but they also are able to see visions of Gray (Ian Alexander), the previous host to Adira's symbiote — something that's also never happened with the Trill in Star Trek before. Adira and Gray were in love, but Gray was killed leading to his symbiont joining with Adira.

Let's talk about previous Trill precedent and how this new story changes those precedents entirely.

The process of joining isn't easy. Potential hosts basically have to go to Trill boot camp to even be considered for joining. Once host and symbiont are joined, they cannot be easily separated. If they are, it's possible that both entities will perish. Given those serious limitations, can human beings (or any non-Trill species) act as host to Trill symbiont? We get what has been the standard canon for decades of Trek lore in the first appearance of the Trill.

In "The Host," we are introduced to Odan (Franc Luz) an ambassador seeking to mediate an ongoing conflict between the Alphans and Betans of the Pelians. When Odan is mortally injured, Dr. Beverly Crusher (Gates McFadden) becomes the first member of Starfleet to learn about the existence of the Trill symbiont. Before Odan dies, it is decided that Commander William T. Riker (Jonathan Frakes) will be temporarily joined with the Odan symbiont until a new, permanent host can arrive.

While Riker acts as host to Odan successfully at first, he experiences life-threatening side-effects almost immediately. While Crusher is able to give Riker immunosuppressants to reduce the effects, the truth is clear: The human immune system will fight the symbiont and force it to either leave or die.

Adira, on the other hand, suffers no physical maladies from the joining — at least none that we're aware of. Their only side-effect is that they temporarily lose some of their memories as a result of the specific emphasized by the joining. The only difference that we're aware of is that Adira and Gray are in love. With the Trill homeworld in peril on Star Trek: Discovery, this huge change to the lore is a potentially life-saving one for the Trill going forward.

The Trill changed a lot once Star Trek: Deep Space Nine came along. The trademark Trill spots didn't even exist when Odan appeared on TNG, but there is still another major change from Discovery we have to address, and that pertains to previous hosts.

The way the Trill joining works doesn't really hold up under scientific scrutiny — it's at least as much spiritualism as it is science. Which brings us to our next, big question: Can Trill hosts communicate with previous hosts? The answer is yes, but Discovery takes the precedent originally set much further. In the final season of DS9 Ezri Dax (Nicole de Boer) connects with a previous host consciousness named Joran Dax (Leigh Joseph McCloskey) in the episode "Field of Fire."

In order for Ezri and Joran to communicate, Ezri must first perform the Rite of Emergence, a psychic ritual which allows the previous host to call upon and interact with a previous host. Joran Dax is a very specific example. All of the Dax hosts dismiss the existence of Joran because he is a murderer, but Ezri requires his help as she investigates mysterious murders throughout the station.

"Field of Fire" is a transaction. While Ezri will ultimately remember Joran in ways the previous Dax hosts did not, she only speaks with him in this one instance ,and only as the result of a specific ritual.

Long story short: It is a very big deal that Adira and Gray can communicate in a ongoing fashion and without the use of any formal rituals.

Let's put everything together in context so we understand what it means that Adira can both have a Trill symbiont inside of them and communicate independently with Gray, a previous host, from beyond the grave.

For Trill in the Star Trek: Discovery timeline, this is a huge deal because Trill is in a state of collapse. Without Starfleet or the Federation around, the Trill homeworld has closed itself off and there simply aren't many joinings happening. If other races can join with Trill symbionts and communicate with past hosts, that's a gateway in two directions — it both gives the Trill a path forward with other species again and it gives the Trill access to important knowledge and experiences of their past they need to understand how to survive in a timeline fraught with conflict.

Likewise, for fans this is also a big deal because it means we could potentially see a character folks have wanted back for decades now — Dax. At the very least, it's possible and even likely that a new actor could take on the role of a new Dax joining. It is also possible that if someone joins with the Dax symbiont that fans could see appearances from former actors who have played Dax on DS9. That could mean cameos from both Terry Farrell as Jadzia and Nicole de Boer as Ezri Dax.

If nothing else, the return of these two actors, even briefly, would be tremendously cool for long-time fans of Deep Space Nine, but, for Star Trek in general, Adira and Gray's connection on Discovery changes almost everything about how we've seen the Trill so far.