Halo Season 2’s Massive Forerunner & Human Connection Explained

Spoilers are ahead for Halo season 2, episode 7.

In Halo season 2, episode 7, “Thermopylae,” Dr. Catherine Halsey (Natascha McElhone) reveals a massive Forerunner and human connection — one that has story-altering implications for future installments of the Paramount+ series. After landing on Onyx, a planet with a secret Forerunner connection, Dr. Halsey snuck off to the site of a hidden UNSC research facility. Thanks to her troubling visions, Kwan Ha (Yerin Ha) accidentally follows Halsey down the proverbial rabbit hole — and into the underground facility where, Halsey says, “it all began.“ While episode 6 keeps the “it” vague, “Thermopylae” shines light on Halsey’s cryptic line.

When Dr. Halsey claims the installation’s tunnels have changed — walls crop up in places she claims they weren’t all those years ago — the unlikely duo follow Kwan’s visions of The Mother (Olwen Fouéré) to the heart of the facility. There, Olive Gray’s Commander Miranda Keyes, Halsey’s estranged daughter, greets her mother by taking a jab at her research “mistakes.” While Miranda is working tirelessly to solve a Forerunner puzzle and open the door her mother couldn’t unlock, Dr. Halsey reveals more about what she was toiling away on during her previous stint in the Onyx research facility.

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Dr. Halsey Reveals The Forerunners Had Ancient Human DNA

Although Dr. Halsey wasn’t able to fully unlock the secrets of the strange Forerunner site in the heart of Onyx, she did learn a thing or two while researching the artificial planet. Rife with Forerunner technology, the ONI-controlled planet actually inspired much of Halsey’s subsequent research. When Miranda probes her mother for information, Halsey is reluctant to share her past findings. Eventually, she uses the reveal as leverage to get Miranda, who’s equally excited about the Forerunner tech, to work with her. The UNSC scientist shares that she found DNA in the Forerunner site.

To make matters more compelling, Dr. Halsey uncovered multiple strands of DNA — “theirs and ours,“ as she puts it. While it makes sense that the Forerunners had access to their own genetic material, it’s surprising to hear that they had the DNA of humans too. Presumably, the DNA Halsey found was that of ancient humans — before they were wiped out. Still, the discovery prompted Dr. Halsey to deeply consider the next stage in human evolution. Clearly, her findings on Onyx became all-consuming ones, especially considering the origins of the Spartan-II program.

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Dr. Halsey’s Discovery Of DNA On Onyx Shaped The Spartan-II Program

In discovering both the DNA of ancient humans and the Forerunners who built the installation on Onyx (and, if the Silver Timeline aligns with the core canon, Onyx itself), Dr. Halsey was inspired. Much of Halo season 2 has hinged on Dr. Halsey’s ethics — or lack thereof — when it comes to the Spartan-II project. In fact, James Ackerson (Joseph Morgan) made the Spartan-III program his life’s work after Halsey’s methods of dangerous genetic augmentation killed his would-be supersoldier sister, Julia (Bronte Carmichael). Even after everything, Dr. Halsey’s dedication to her science remains unwavering.

The UNSC scientist’s findings on Onyx were too important for her to record in a journal. As Halsey explains to Miranda, the discovery of both DNA strands not only opened the door to new research, but prompted Halsey to search the galaxy for humans with certain genetic markers. Given Kwan’s cutting remark about Halsey abducting children, it’s safe to assume that Dr. Halsey used the Forerunner and ancient human DNA findings in order to craft her Spartan-II program and, potentially, seek out the Covenant’s “blessed ones” like John (Pablo Schreiber), who are able to activate Forerunner technology.

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Halo Season 2, Episode 7 Finally Explains Dr. Halsey’s Halo Season 1 Ending

In Halo season 1’s ending, Dr. Halsey provides a chilling voice-over to close the episode. The UNSC scientist and Spartan-II program creator believes that the Halo holds the secret to human transcendence. As a result, she wants to continue to seek it out, reiterating that she’s just as pressed to find the Sacred Ring as the Covenant. Unlike Admiral Parangosky (Shabana Azmi) and other ONI and UNSC higher-ups, however, Halsey wants to discover the Halo’s potential for guiding human evolution. Clearly, the discovery of the DNA strands on Onyx left a lasting impression on Halo‘s leading scientist.