Summary

• William Shatner's rejected Star Trek: Enterprise comeback would have featured a captivating Mirror Universe storyline involving an older and more sinister version of Captain Kirk.
• The proposed episode would have seen Captain Jonathan Archer and the crew of the NX-01 Enterprise stumble upon a pocket universe where evil Kirk and other banished individuals had formed a community.
• With evil Kirk, played by Shatner, at the helm, the story would have revolved around a prison escape plot as they attempted to take control of the Enterprise and escape with their minions in tow.

William Shatner's rejected Star Trek: Enterprise comeback was an amazing Mirror Universe storyline, which was explained by Enterprise's late showrunner, Manny Coto. Shatner's Captain James T. Kirk was killed off in 1994's Star Trek Generations, and Bill said farewell to his signature character. However, a decade later, an idea was hatched by Shatner and writers Judith and Garfield Reeves-Stevens to bring a different and nefarious version of Kirk from Star Trek: The Original Series to battle Captain Jonathan Archer (Scott Bakula) and the crew of the NX-01 Enterprise.

In the oral history "The Center Seat: 55 Years of Star Trek" by Peter Holmstrom, Manny Coto detailed the proposed storyline for William Shatner's guest appearance in Star Trek: Enterprise season 4. Coto and Star Trek producer Rick Berman met with Shatner and heard his comeback scenario, which Coto loved. Read his quote below:

The idea was it was a Mirror Universe-themed episode. In the original “Mirror, Mirror,” the evil Kirk had a device that was called the Tantalus field, which you press a button and his enemies would vanish. Now, it was implied in there, in that episode, that they just kind of died, but what the Reeves-Stevenes were saying [was], “What if what this field did was transport everyone who was opposed to him into this pocket universe?” So, they were all on this planet surviving. At the end of that episode, it’s implied that the good Kirk had convinced the evil Spock to take command from the evil Kirk. And Kirk told him about the Tantalus field. So you would have surmised that at the end, the evil Spock would have sent Kirk to the Tantalus field [and taken] command of the Enterprise.

So now you have this pocket universe with the evil type we were calling Tiberius Kirk kind of stranded with other people who evil Spock has banished. But they’ve forged this kind of community in basically a prison. The idea was what if Archer and the Enterprise stumbled into this pocket universe and evil Tiberius Kirk was now an older man, but still formidable, and wanted to take control of the Enterprise and escape. It was a prison escape. So it would have been evil Kirk, William Shatner, Tiberius, trying to take over the Enterprise with other minions who had been trapped there.

William Shatner's Star Trek: Enterprise Comeback Was Rejected By Paramount

Paramount rejected William Shatner's proposed Star Trek: Enterprise comeback. According to Manny Coto in "The Center Seat," the studio didn't want to pay Shatner what he was asking for, which Star Trek producer Rick Berman agreed was more than the series could afford. However, Coto believed that "[Paramount] wanted [Enterprise] to die" and that the studio didn't hire Shatner "not because he was too expensive, but because they might've saved the series. That's my conspiratorial thinking."

Manny Coto got to do a Mirror Universe two-parter in Star Trek: Enterprise season 4, and it was during production of "In the Mirror, Darkly," that the cast and crew of Enterprise were informed the series was canceled. William Shatner playing a Mirror Universe Kirk and fighting Captain Archer would have certainly been an event Star Trek fans would have tuned in for, which Coto thinks would have been "classic Star Trek, and a glorious piece of Star Trek that would now exist."

Source: "The Center Seat: 55 Years of Star Trek" by Peter Holmstrom