Ep 15. The Fifth Race

Opening with a standard SG-1 mission briefing, Colonel O'Neill and his team are tasked with exploring a new planet with what they expect to be a "simple milk run". However, their expectations are quickly dashed as they are ambushed by a group of aliens who appear incredibly advanced, but immediately back off and seem to show immense respect to a piece of ancient technology Jack obtains by mistake.

Meanwhile, SG-1's resident genius, Samantha Carter, is working on a way to decipher and use an ancient alien language that they've been encountering since the beginning of the series. However, the task proves more difficult than expected, and Carter is approaching a wall when Jack contacts SGC to bring back the ancient artifact he found.

Back on Earth, Jack connects himself to the device, which instantly pulls up a massive amount of information and knowledge that seems to be directly downloaded into his brain – but at a cost. He passes out, and upon waking up, he can't remember who he is or how he got there. The SG-1 team is horrified, and they try various methods of retrieving Jack's memories, but it seems all is lost. However, the alien race from earlier comes to Earth and, through the language that Carter was working on, explains to the team that the device is a repository of information from a long-dead race of advanced people, and they had long since lost the key to accessing it.

Now, with Jack's brain being the only key they have, SG-1 is in a race against time to take down essential data before their injured, disoriented teammate passes away from the stress. Once again, Samantha Carter is called upon to translate the alien hieroglyphs that continue to appear in Jack's mind. It's a difficult task, but she proves equal to the challenge as SG-1 explores the staggering amount of knowledge available to them.

Meanwhile, the alien race teaches the humans that they, in fact, are the legacy of the long-dead Ancient people who built the device. Using the knowledge they've gathered, they've managed to piece together their former civilization and keep pushing the boundaries of space exploration. As the episode reaches its conclusion, SG-1 uncovers a shocking revelation about the history of the galaxy and Earth's place in it.

In the end, O'Neill manages to regain his memory and sets a course for a far-off planet. SG-1's mission is far from over, and the newfound knowledge they've acquired will allow them to better protect Earth from the numerous threats they face. The Fifth Race is a standout episode in the Stargate SG-1 series, expertly blending sci-fi elements with mystery and adventure, leaving viewers on the edge of their seat until the very end.