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SG-1 faces creatures of mass destruction that even the Asgard can't control, and must destroy Thor's infested vessel before the Replicator bugs reach Earth.

FAN RATING - 9.32 
DVD DISC: Season 3, Disc 5
WRITTEN BY: Robert C. Cooper
DIRECTED BY: Martin Wood
GUEST STARS: Colin Cunningham (Major Davis), Gary Jones (Technician), Guy Lee-Frazier (Technician #2), Michael Shanks (Voice of Thor)
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With Daniel Jackson recovering from an emergency appendectomy, SG-1 is on vacation. Sam finally has the time to catch up on some of her research, Teal'c is off-world visiting his wife and son, and O'Neill is about to leave for a fishing trip to Minnesota.

But Thor, the powerful Asgard commander, has other plans. His ship, the Beliskner, has been overrun by what the Asgard call "Replicators" – technological insects that self-replicate and infest ships, planets, even entire systems. This is the great enemy with whom the Asgard are at war ("Fair Game").

The Replicator bugs have taken over the Beliskner and attacked Thor. They learned of Earth from the computer's database, and brought the ship there. The crew was left behind, but Thor destroyed the outbound transporter system and remained on board to try and stop the bugs from reaching Earth. Now that he has failed, he transports Colonel O'Neill to the ship to try and destroy the vessel before the Replicators land it and overrun Earth.

Jack learns that Thor is alone on the Beliskner and near death, and recognizes that he must destroy the ship – and die with it. He contacts the S.G.C. and requests a load of explosives, which he transports up. But against his orders, Teal'c and Major Carter arrive on the ship with the supplies.

Carter believes she has found a way for them to get off the ship after they crash it into Earth's atmosphere: a space shuttle is on the launching pad prepared for an emergency pick-up. The team battles the techno-bugs as they venture through the ship's corridors and back to Thor's chamber.

Teal'c and O'Neill locate the ship's bridge in an attempt to regain control of the navigational computer, but find it overrun with Replicators. Their only hope at destroying the Beliskner is to place naquadah-enhanced explosives outside the ship on the deceleration drive. Once the Replicators have built up their forces and attempt to land the ship, SG-1 will detonate the bomb and cause the ship to burn up in the atmosphere.

Still battling the seemingly invincible Replicators, the group puts the dying Thor into stasis and finds a new way to escape the doomed ship. They use the still-functioning inbound transporter to steal the S.G.C.'s Stargate. Fighting off wave after wave of bugs, O'Neill, Carter, and Teal'c dial the gate to P3X-234 and escape with Thor.

On Earth, General Hammond and Dr. Jackson watch the Stargate disappear, and figure out the team's plan. They're going to dial back to Earth and arrive through the second Stargate ("Touchstone"). Hammond orders it unpacked and made ready to use immediately.

The Beliskner crashes into the atmosphere and is destroyed. Fragments of the ship's hull crash into the Pacific Ocean, 400 miles off the coast of California. Naval teams are ordered to the site to recover the debris.

But at least one Replicator has survived the crash. It crawls out of the water and onto a chunk of debris, floating in the middle of the ocean and waiting for the Navy ships to arrive.


  • Carter has been studying the decay rate of naquadah within the S.G.C.'s naquadah reactor (built in "Learning Curve").
  • Teal'c was off-world visiting his wife, Drey'auc, and his son, Rya'c. The two live in the "Land of Light" ("The Broca Divide", "Family").
  • The Replicator bugs are attracted to high bursts of energy (such as the Asgard transporter). They are also impervious to zat gun discharges. They reassemble after being hit with a shotgun blast, but a second blast may successfully destroy them. Teal'c looked down the hallway as the team fled from the twice-blasted bugs, and did not see them regenerate.
  • The bugs replicate by consuming the metal alloys of the ship. They appear to excrete a digestive fluid to accomplish this.
  • The Replicators are the great enemy of the Asgard – the reason given by Thor as to why the Asgard could not get involved in a war against the Goa'uld ("Fair Game"). They were discovered on an isolated planet in the Asgard's home galaxy. The creators were not present, likely destroyed by their creation. The Replicators were brought aboard an Asgard ship for study before the Asgard realized how dangerous they are.

    The Replicators learned from the technology employed by the Asgard to destroy them, and have become a plague on the Asgard's entire galaxy, annihilating everything in their path. Thor said that the Asgard's overconfidence in their technology has become their undoing. In this way, they are similar to the Tollan, who were almost destroyed by the Goa'uld because of their arrogant over-confidence in their own advanced technology ("Pretense").
  • The Replicators' odds of survival in a new environment depend on numbers, according to Thor. This may be the key to their defeat on Earth, if only a few survived the destruction of the Beliskner.
  • Each bug is capable of individual behavior, yet they all act with a common purpose: self-replication. They are highly capable of learning and adapting.
  • The first thing that the Replicators do when they board an Asgard ship is disable the sensors capable of detecting them. They cannot be detected by thermal sensors – meaning they must not give off heat.
  • The Russians have been placed on alert, but do they know what they are looking for? Have they been informed about the Stargate program and the Asgard?
  • The Stargate has a total of nine chevrons, including two at its base not used for standard activation, and usually not seen. The eighth chevron adds an additional distance calculation, enabling O'Neill to travel to the Asgard galaxy Ida a year ago ("The Fifth Race"). The function of the ninth chevron remains a mystery.
  • With the second Stargate installed at the S.G.C., the facility may be temporarily vulnerable to other threats. A permanent iris was welded to the gate ("Touchstone"), which no doubt must be removed to make the gate operational. But how long will it take before a functioning iris can be attached? Until then, anyone may dial Earth's Stargate and come through unhindered.
  • At least three Replicators can be seen walking on the Stargate after Teal'c establishes a wormhole with P3X-234. They may have been destroyed in the blast, or they (and others) may have gone through the gate with SG-1.


  • Asgard ships are equipped with sophisticated cloaking technology. (This explains why Asgard ships have visited Earth often without ever being detected.)
  • All Asgard ships are equipped with an internal dampening field that activates in case of an explosion.
  • Asgard ships also have force-fields outside the hull. (The Goa'uld also possess this technology ["Within the Serpent's Grasp"].)
  • The Beliskner – Thor's ship and the flagship of the Asgard fleet – is powered by four neutrino-ion generators, and propelled by two rear thrusters.
  • Asgard ships have internal transporters.
  • The Stargate is hooked up to power generators in the S.G.C., but once removed the gate itself retains enough power to dial out once without an attached power source.


  • Jack O'NeillJack O'Neill - O'Neill has a growing and personal relationship with Thor, and quickly recognized that he had been called upon to give his life to save Earth. Jack, ever the hero, was willing to face this fate.
    O'Neill invited Carter to go fishing with him on their vacation time, and seemed a little anxious to accept her refusal. Sam almost certainly has some level of romantic interest in Jack ("A Hundred Days"), but Jack has never really expressed such interest in her. He does consider her a friend, and more than just a fellow officer, but may also know of her affection for him.
  • ThorThor - Thor's ship was called into battle against the Replicators, and infested with them. He left his crew behind, and tried to stop the Beliskner from reaching Earth. Having failed, he condemned himself, his ship and Colonel O'Neill to death in order to stop the bugs from reaching Earth. Thor is now near death.
  • Daniel JacksonDaniel Jackson - Forced to stay behind on Earth because of his surgery, Jackson felt the loss of being unable to join the rest of SG-1 on the Asgard ship. He felt like he should be up there, with his teammates.
  • Paul DavisPaul Davis - Davis, who serves as the S.G.C.'s liaison at the Pentagon, is dedicated exclusively to the Stargate program.


  • If O'Neill was on vacation, why would he not choose to visit Laira, the woman he loves, on Edora instead of fishing alone in Minnesota ("A Hundred Days")? Does he consider their relationship over?
  • Was Thor attacked by the bugs? Why exactly is he dying? They don't seem to be pursuing him, or paying him much notice.
  • What is the ninth chevron used for? The eighth adds an extra distance calculation, allowing a Stargate to establish a wormhole outside our galaxy. Could the ninth allow a traveler to go even farther? Or to another dimension? Or through time?
  • Who created the Replicators? Where are they now? Were they wiped out by their creation, as Teal'c speculated?
  • Are the Replicators really the great enemy of the Asgard, as O'Neill speculated?
  • Will the Replicators gain a foothold on Earth and begin to spread?
  • What planet is P3X-234? Why did Teal'c choose that as their escape destination?
  • Has the first Stargate been destroyed? If not, how will O'Neill, Teal'c and Carter return to Earth if it remains the dominant gate for receiving incoming wormholes?
  • Can Thor's life still be saved?
  • Did O'Neill, Carter and Teal'c escape the ship before it was destroyed?


  • Daniel Jackson's surgery was written into the script of "Nemesis" to accommodate actor Michael Shanks, who came down with appendicitis at the time of filming. "I remember coming up with some elaborate reason Daniel wasn't in that morning's scene and pitched it to Rob [Cooper]," executive producer Brad Wright later recounted. "He said, 'Why don't we just say Daniel had appendicitis?' I said, 'That's GENIUS!'"