Simply put, "Past Tense I" is one of the best episodes of the series. It works terrifically as a refreshing time-travel story (the first for DS9) as well as a provocative allegory, characterized by heaps of brilliantly realized character moments. Sophomore director Reza Badiyi gets a chance to shine two months after helming the relatively pedestrian "Civil Defense."

A transporter mishap sends Sisko, Bashir and Dax centuries into the past to a point in time just days before a violent incident that will lead to a turning point in Earth's history. Now they must find a way back to the 24th century, being sure to avoid disrupting the time-line while in the past.

Sisko and Bashir wake up on the streets of San Francisco in the year 2024, finding themselves separated from Dax. Caught by the police without ID, the two are placed in a "sanctuary district"--an isolated section of the city composed of thousands of homeless, jobless, poverty-stricken citizens.

Before long, Sisko, an avid history buff, realizes that he and Bashir have landed just days before the infamous Bell Riots--one of the most violent civil disturbances in American history, scheduled to unfold within the very sanctuary district where the two have become prisoners. History states the event begins with district residents taking hostages at the processing center. It ends with armed forces killing hundreds of innocent people in an attempt to secure the situation as it turns into a rally. A man named Gabriel Bell plays a pivotal part in the incident by sacrificing himself to ensure the safety of the hostages. Sisko tells Bashir the incident will cause public outrage of the nation's condition and a major step forward to solving Earth's social problems.

Brooks and El Fadil both deliver memorable performances, and the pairing of their characters provides a poignant subtext: Sisko as the wise teacher from a future that remembers its past, and Bashir as the student whose eyes are opened to grim, depressing history for the first time.

When the two have an unexpected confrontation with street thug B.C. (Frank Military), a fight leads Gabriel Bell to intervene. B.C. kills him in the brawl, thus altering the future. Without Bell to save the hostages and take his proper role in history, Sisko realizes that it is imperative he and Bashir make sure history unfolds as it should. When B.C. takes the hostages in the episode's closing minutes, Sisko decides he must take Bell's place in history even if it means sacrificing himself in the process.

The most notable aspect of "Past Tense I" is how it affects Sisko's character. It's nothing short of a breakthrough as the writers put him into an extremely volatile situation and allow him to make monumental decisions. The results are Sisko's best actions yet as DS9's leader and hero. This is the Sisko that's been in the making for two years now. Sisko's decision to take Bell's place is an act of heroism that deserves to go down in Trek history right along with Kirk's saving of Earth in Star Trek IV.

And as a social commentary, the episode is intelligent and effective. Set in what we would call the near future, homelessness and economic problems have escalated to the point where the urban unemployed are merely shoved into these districts (prisons would be a better description) where the government and more fortunate can simply forget they exist. Some gritty production design and interesting photography set the tone, turning a few city locations into a fairly convincing reality.

In addition, the B-story is sensible and subtle, characterized by some details that make a difference. Dax is found unconscious by communications executive Chris Brynner (Jim Metzler), who gives her access to a terminal she quickly uses to establish a proper 21st century identity. It's interesting how Dax winds up with people on the opposite end of the economic scale (Brynner is a multi-millionaire who hosts upscale business parties). Dax has a discussion with some of Brynner's snobbish friends that reveals the general public's uncaring attitude on the sanctuaries--one party guest dismisses them as "the only way to keep those people off the streets." Brynner comments that the sanctuaries exist solely for the residents' benefit, but he can't offer an answer when Dax asks why there is a wall around it.

Resembling The Original Series episode "City on the Edge of Forever" in many respects, this installment redelivers the poignant nature of the concept and remains true to the idea (with exception to the obligatory '90s Trek time-travel technobabble). Delivering on-target drama while keeping every element of the plot in sync, "Past Tense I" is a season highlight.

Previous episode: Fascination
Next episode: Past Tense, Part II