Production on Season 4 reached the halfway point this week with the completion of "Observer Effect," the 11th show of the year out of 22, and the first episode set to air in 2005.

Written by Judith and Garfield Reeves-Stevens, "Observer Effect" is a simple science-fiction tale relying entirely on the actors' performances for its production value, with a dollop of classic Star Trek sensibility. Trip Tucker and Hoshi Sato return from an away mission with a grisly virus which appears to be incurable and could easily infect the rest of the crew. Meanwhile, unbeknownst to Archer and company, noncorporeal aliens are occupying the bodies of officers in order to observe and judge the humans' responses to the viral threat. The aliens fully expect some if not all of the crew to die. (Apparently flu shots are in short supply in the future too.)

This is the second episode in a row (after "Daedalus") considered a "bottle show" because the story takes place entirely on existing ship sets. This one, in fact, doesn't even have guest stars (there tends to be one episode per season like that — "Shuttlepod One," "Dead Stop," "Doctor's Orders"). As mentioned in the last production report, bottle shows are scheduled every now and then to give the crew and the budget a rest, but they also compel the writers to come up with stories that are strictly character-based and focus more attention on the principal cast. In this case, all seven of the actors have a significant role.

In keeping with showrunner Manny Coto's mandate that this season will help connect Enterprise with the original Star Trek, this is the NX-01's second encounter with noncorporeal beings (which seem to be around virtually every corner in Captain Kirk's day). And like in "The Crossing," the actors in turn take on the personalities of these entities. This time, however, there are two distinct characters with specific attitudes, which jump from one pair of crewmembers to another, so the challenge for the cast and director Mike Vejar was to keep the personalities consistent.

Principal photography began Friday, October 22, and ran the usual seven days until this past Monday. Most of the shooting took place either in Sickbay or the Decon Chamber, where Trip and Hoshi are quarantined. There was one Shuttlepod sequence, plus scenes in an Airlock, Corridors, Turbolift, the Mess Hall and the Bridge. An Auxiliary Medical Lab swing set was put together for this episode. A number of additional medical props were brought into Sickbay, including a 22nd-century defibrillator. The makeup people worked on Linda Park and Connor Trinneer to give them three stages of sickness in different scenes. Scott Bakula and John Billingsley wore EV suits in certain Sickbay scenes where matters get really serious.

Another reason for a bottle show is to give the visual effects team some breathing room to complete the demands of prior episodes. In the midst of this schedule Dan Curry directed a second unit on an adjacent soundstage to gather pick-up shots for "The Forge" (airing in two weeks). Jolene Blalock was borrowed from the principal unit for one greenscreen scene, but mostly stand-ins and hand doubles were all that were needed for inserts involving digital effects.

This is the second script for the Reeves-Stevens couple, prominent Trek authors who joined the Enterprise staff this year. "The Forge" was their first. Vejar, a regular on every Trek set since The Next Generation, last directed "Cold Station 12," which will be seen this Friday.

"Observer Effect" is tentatively scheduled to air January 7, 2005. (There will be reruns on Christmas Eve and New Year's Eve, thus far unspecified.) Updates will be posted in Episode Detail closer to showtime.