In our world, actress Gates McFadden played Chief Medical Officer Doctor Beverly Crusher on Star Trek: The Next Generation for every season except the second, when she was temporarily replaced by Diana Muldaur playing Doctor Katherine Pulaski. Covering the behind-the-scenes drama causing McFadden's (and Crusher's) temporary absence from the USS Enterprise is beyond the scope of this thought experiment, to wit: What if Gates had not returned for seasons three through seven? And what if Diana Muldaur declined to become a series regular, leaving after season two?
Enter Anne Twomey
Imagine if the showrunners dipped back into the well of previous actresses who auditioned for the Pulaski or Crusher roles. Imagine further they took a second look at Anne Twomey, who auditioned for Crusher a couple of years before. In this reality, Twomey plays Doctor Rachel Arbogast.Doctor with a Difference
To differentiate Arbogast from Crusher and Pulaski, the showrunners give Arbogast a wacky sense of humour; she loves to pull pranks, insert puns into conversations, and tells Mom jokes (though she's not a mother). They also give her a darker backstory than either of the show's previous CMOs. She doesn't warm to the other series regulars until several seasons have gone by, nor they to her, seeing as they've already gone through two CMOs. Wesley Crusher, in particular, is initially the most standoffish.
As the third season unfolds, we learn Arbogast spent several years ships on the front lines of a mysterious, little-spoken-of war; she survived some gruesome encounters and pulled a lot of people through grave injuries. She lost a lot; maybe she lost everything. She doesn't talk about it. It's in her service record, but you'd never know it coming from her; Riker, Picard, and Troi are the only ones who know the full details, but the other characters (and the audience) won't learn her whole story for a while.
Alternate Episodes
In many episodes, the show doesn't require a specific character or actress to carry out the role of doctor; any medical professional would do. But in certain episodes, Crusher's replacement by Arbogast would make a difference. Here are a few examples:
In the real-world version of "Evolution," the show's season three premiere, Doctor Crusher's return is briefly explained and she enjoys a warm reunion with her son Wesley. But in this version, there's no Crusher and therefore no reunion. Instead, we meet Arbogast when she's called upon to treat Dr. Stubbs, the episode's guest star. Maybe she gets a few extra moments of character development in a meeting with Picard; Crusher and Picard had a short conversation about her return, so there's time in the episode to give the audience a bit of a backgrounder on Arbogast. And maybe the rest of the episode continues as normal; at this point, with the show on doctor number three in as many years, the producers might not yet have decided if Arbogast is going to be a major character or not. Perhaps she gets a scene with Guinan at the end of the episode, just as Crusher did in the original timeline.
In "Who Watches the Watchers?", maybe Rachel refuses to mind-wipe the Mintakan, Liko. This doesn't change the outcome of the episode, but gives us a bit of insight into Arbogast's character; she's seen such terrible trauma that she refuses to inflict injury on a patient, no matter what the cost. This puts her in conflict with Picard and the Prime Directive, and puts her position (in the real world and the world of the show) in jeopardy. We wonder how long she'll stick around.
In "The Enemy," Worf's decision to refuse to donate blood to save the injured Romulan results in a long-standing low-key animosity between Arbogast and Worf. Unlike Crusher, Arbogast doesn't have much history with Worf at this point, so her opinion of him is tainted by a decision she must accept as a medical doctor, but privately disdains as a matter of principle. Hard to imagine the TNG writers allowing TOO much tension among characters in the main cast, but maybe they'd allow the thread to play out just a little, at least until events in a later episode cause Rachel to re-evaluate Worf.
"The High Ground" would be Dr. Arbogast's first big episode, since she's the one that gets kidnapped by Ansata separatists on Rutia IV. Maybe she's more sympathetic than Crusher was to the Ansata point of view; perhaps her experiences on the front lines showed her that sometimes "terrorism" was the last resort of a subjugated people. In fact, we might uncover hints that the Federation was the aggressor in the unnamed war Arbogast participated in. But while she may have some sympathies, Arbogast knows what side she's ultimately on, and for the first time we see that she's no stranger to combat, taking a much more active role in the climactic rescue than Beverly did. Maybe Arbogast is the one that kills Finn, forced to because he was drawing a bead on Picard.
In "Deja Q," perhaps Arbogast treats the de-Q'ed Q a little more warmly than Crusher did in our timeline, since this will be the first time she's met him.
In "Hollow Pursuits," Arbogast is less disturbed than her crewmates to find she's objectified in Barclay's hologram, and the episode ends on a dry, suggestive coda: "Let me know if you ever want to try the real thing, Reg."
There's no romantic plot for Arbogast in "Transfigurations," but from this point forward she develops a strong interest in transhumanism, something most humans in Trek seem to frown on, given the evidence of the various shows.
In "The Best of Both Worlds" Arbogasts's role is functionally identical to the one Crusher played, but she's more calculated and determined on the away team mission to the cube, though the end result is the same; failure to rescue Picard. And like Crusher, she removes Picard's Borg implants in Part II.
In "Family," we learn what happened to Arbogast's last commanding officer, the woman who was her best friend and spiritual sister. A holodeck conversation with that officer's avatar reveals something of Arbogast's trauma to the audience, but not to the other characters, providing a bit of dramatic irony for seasons to come.
"Remember Me" simply doesn't happen in this version of the show. Instead, the producers go for a different bottle episode, a Troi-centric story that has the counselor guiding a severely wounded but recovering security officer through his PTSD--a rare opportunity to see Troi performing her official function.
In "Data's Day," Arbogast introduces Data to the art of the prank, mostly because she thinks it's hilarious that Data just won't get it.
In "Q-Pid," Arbogast quips "Now I see why you guys find this maniac so annoying." She also uses a rapier in combat instead of a clay pot.
In "The Host," Arbogast isn't fazed at all by the Trill life cycle. Of course she and Odan still part ways by episode's end, but only because Arbogast has to stay on the show. The conclusion has more of a "It was a fun ride!" vibe.
Arbogast doesn't entirely agree with the choices made by "The Masterpiece Society," but following on from her interest in transhumanism established in "Transfigurations," she considers staying behind, in contrast to the Society members who decide to leave thanks to the influence of the Enterprise crew. In the end she decides not to stay on the colony, but because their approach to transhumanism isn't quite radical enough for her...
"Ethics" reinforces the chilly relationship between Arbogast and Worf, but only in lines like "Mr. Worf and I might not get along, but damned if I'm going to risk his life on your experimental treatment." But surprisingly, Worf opens up to Arbogast during a consultation. "I have seen the warrior's fire in your eyes and in your actions. You hide it well, but you know that I cannot live like this. Because you could not live like this." Arbogast realizes Worf is right, and cooperates with Dr. Russell. The operations succeeds, but without the death fakeout of the original version of the story. Arbogast berates herself for working with Russell, going as it does against her professional ethics, but this feeling is tempered by a feeling that sometimes the ends justify the means.
"Realm of Fear" turns out pretty much the same, but with some more flirting from Arbogast toward Barclay as she treats his "transporter psychosis."
"Chain of Command" reveals that Dr. Arbogast makes a more badass commando than Dr. Crusher, but the episode goes pretty much the same was as in our timeline.
"Suspicions" reveals Arbogast to be even more stubborn in her pursuit of the truth behind Reyga's death.
When Picard and Arbogast are "Attached," Arbogast learns how much Picard misses Dr. Crusher, which explains, perhaps why he's never warmed to the woman who took her place. Picard learns, finally, the full truth of Arbogast's heretofore hinted-at past, and it drastically changes their relationship - perhaps even calling into question Picard's original choice to have Arbogast replace Pulaski. They form an uneasy understanding by episode's end, but the tension will remain for the rest of the series. Note that only Picard knows what happened - the audience isn't privy to this information.
In "Parallels" Arbogast doesn't appear--but Gates McFadden returns as Doctor Crusher in several of the quantum realities visited by Worf.
"Sub Rosa" relies completely on Crusher's backstory, so it's replaced by "Uncomfortable Truths," a bottle episode in which an old colleague of Arbogast visits the Enterprise and accidentally reveals a shocking truth: during a battle in the mysterious war hinted at in earlier seasons, Arbogast was forced to choose between blowing up a starship with a full crew infected by an insidious biological weapon or trying to save the crew and risking infection of the entire Federation.
We learn that against the orders of her commanding officer, Arbogast beamed a photon torpedo into the engine room of the infected ship, destroying it and killing all aboard. A turning point in the war, this act proved the Federation's resolve in the eyes of the enemy, who agreed to a brokered peace. Only this prevented Arbogast from being cashiered, especially when it was discovered that Arbogast herself had dismissed a potential cure proposed by one of her colleagues - a treatment that, further experiments later proved, would have worked.
Picard, of course, learned all this in "Attached," and he shares his prior knowledge with his senior officers, each of them dealing with conflicting emotions. Worf is surprisingly supportive, given that Arbogast made a "warrior's choice." Data is sympathetic, given that her choice was logical with the information and choices she had at the moment. Riker, Troi, and LaForge are horrified and acknowledge it will make their working relationship with Arbogast difficult.
Arbogast decides to leave, not being able to bear the umbrage of people she's grown to love and respect. She and Picard share one last scene in the transporter room. "What will you do now?" he asks. "I failed because I was human," she says bitterly. "I'm going to see if I can rectify that." Picard shakes his head in sorrow, but knows she's made up her mind, and beams her over to the USS Kurzweil. In the transporter room of the Kurzweil, an unseen figure greets her: "Dr. Arbogast. Let's talk about your future."
In the remaining season seven episodes, Suzie Plakson at long last returns as Doctor Selar, newly promoted to take Arbogast's place. She'll go on to appear in all five (!) TNG films.
Arbogast doesn't appear again until "All Good Things," in the portions set 25 years in the future. She serves the same story function as Crusher did in the original episode, but without the Picard/Crusher romance beats; instead, we see that Arbogast has transformed herself into a cyborg--cold and efficient and in control, far from the practical joker of her early appearances. Old Picard is freaked out by this, given his experiences with the Borg, but knows he has no choice but to work with her. The episode plays out pretty much as it did in our world, but with one difference: before Picard joins the poker game, we see him composing a letter to Arbogast, asking her to meet the next time their ships are (relatively) close; he has something important to share about her future.
But with Plakson's Doctor Selar taking McFadden's Crusher role in the four TNG feature films, there's no compelling reason to revisit Arbogast's thread in those films. Instead, she doesn't return--nor does Crusher--until the third season of Picard, where we see that her quest for transhumanity has had tragic consequences--though she goes out a hero...
