The Callisto Protocol invites you to immerse yourself in the story of ill-fated pilot, Jacob Lee as he aims to escape wrongful imprisonment on Jupiter's icy moon, Callisto, that's overrun by inmates and guards infected with a mysterious alien virus.
The Callisto Protocol's plot feels relatively short and straightforward, and the gameplay complements its linear trajectory. However, there's quite a lot of refinement, with several additional layers and details that may have passed you by as you were desperately trying to evade the hordes of infected.
Major plot spoilers ahead.
10 Intentionally Corrupted Robots
Before things suddenly took a turn within the opening moments of The Callisto Protocol, the Black Iron Prison Security Units helped the guards in enforcing the rules and moving prisoners. Once Warden Cole initiated the mayhem of The Callisto Protocol, the robots turned murderous against everyone, even the guards.
These giant robot killing machines seemed to have either a change implemented to their program or something built-in that triggered new directives - not allowing anyone to escape the facility and not harming Biophage creatures. Therefore, the robots were most likely methodically designed with this feature for Cole's Callisto Protocol experiment to fully take shape.
9 Hapless Victim Ferris
Captain Leon Ferris may seem intimidating at first, and someone you grow to hate throughout the game, but he's just as innocent as Jacob in all this. He shows no loyalty to Warden Duncan Cole, and his audio file reveals that he prefers the former warden, who mysteriously disappeared.
Ferris is as ignorant as Dani and Jacob to the UJC's malevolent experiment and is simply there to do his job of handling prisoners at Black Iron. There's no conspiracy between him and Warden Cole, as he himself unwittingly becomes an expendable test subject like the other guards.
8 Life On Other Moons
The Callisto Protocol takes place in the year 2320 and envisions a future where moons like Europa are capable of sustaining human life. Although, it becomes apparent that it's not just limited to Europa, and that the UJC has been busy establishing settlements across Jupiter's other two large Galilean satellites, Ganymede and Io.
If you closely examine the audio Data-Bios that you recover from some of the deceased Callisto personnel, you can see their birthdays and places of birth. A small portion, like Jacob, hails from Earth, but there are also locations for multiple cities found on moons Io and Ganymede. Some names include Jupiter's Rise and Water's End in Ganymede and Aoudaghost in Io.
7 Jacob's Conflicting Subconscious
Protagonist Jacob Lee transports cargo for the UJC and discovers a secret compartment in a crate that contains the Biophage larvae samples responsible for the horrible outbreak on Europa. While it's clear his partner Max Barrow is aware they're playing a part in it, Jacob decides to be oblivious and stick to the job.
The CORE unit implanted to Jacob's neck, courtesy of Black Iron Prison, starts to affect his memories, and he begins suffering strange hallucinations like Isaac Clarke that ultimately represent his guilty thoughts trying to fight off the device that's suppressing them. The purple cube toy belonging to Dani's sister is a lasting image ingrained from the news report, and Max's corpse haunts his mind.
6 The Blind Colony
This one has two meanings to it. Underneath the prison on Callisto lie the remnants of a decades-old mining colony called Arcas, which you explore later on. The deeper narrative surrounding the colonists is that the UJC promised them a vision of new beginnings, but they were unknowingly mining to extract the giant Biophage monstrosity.
The Arcas colonists got blindsided by the UJC and sadly paid for it. Those that survived the purge became the Biophage enemies known as The Blind. They're unlike any of the others you face because the're attracted to sound, showcasing their adaptation to the dark underground environment that resulted from their evolution.
5 Terraforming Efforts
The UJC's original prospects for Callisto didn't involve the mess that has now unfolded. Their mission was one of expansion that sought to terraform Jupiter's moon to make it more inhabitable for humans to thrive. The biodome in the Habitat region of Black Iron Prison shows some extent of what could've been.
There's a lush forest environment, now ruined by the organic matter synthesized by the infected Biophages, and a botanical area where various strains of plants are grown on rotating habitats. Callisto’s terraforming engineer, Miranda Kristofich reveals in her audio log that the UJC spent billions on the project only to terminate it.
4 Varying Evolutionary Effects
The Callisto Protocol is successful at gradually unraveling its narrative through environmental storytelling, and that's even further evident in the design details of the Biophage creatures that stalk you every bit of the way. The overall plot is about searching for the next phase of human evolution, but the pathogen's properties show it isn't uniform.
The variety of infected conveys that the Biophage virus produces different effects depending on the individual's genetic material, creating a brilliant opportunity for having a unique pool of enemies for you to encounter and building on the plot. Some test subjects became mutating tentacled beings, others long tubular-necked creatures in cocoon pods, and many developed conjoined bodies.
3 Not Only Callisto
Among the most shocking revelations throughout the game, it’s evident that the virulent Biophage larvae unearthed at the Callisto Colony site aren't native to the region. Chief Medical Officer Dr. Mahler and an audio log from Arcas Admin Yannick Sage confirmed another planet called Paramo witnessed a similar incident before the tragic outbreak that befell the mine.
They both mention how the ultimate goal is to recreate the "Paramo Effect" on Callisto. This means the giant alien who provides the larvae samples to the UJC exists elsewhere on other ocean planets, or possibly those with different ecology and atmosphere since it readily adapts to any environment.
2 The Commonality's Prophecy
In much the same fashion as Dead Space, the threat behind the Callisto Protocol is an enigmatic cult named The Commonality. One of the leading figures is Warden Cole, and their primary objective is to advance human evolution so that humans can persist in the far reaches of space - starting with the breeding grounds of the prison.
However, there's a greater prophecy at play for Jacob in The Commonality's pursuit. A lore room you access has an ancient tablet on display that depicts a David and Goliath story of a warrior spearing a giant worm-like alien resembling the Biophage one. The Commonality also refers to Jacob as the survivor and "Vir Solitarius," Latin for "lone man," signaling he may be their rival specimen.
1 Hive Mind
The Callisto Protocol sprinkles enough evidence to suggest that the mutated Biophage subjects behave under a hive mind. The case of Subject Zero from the original Arcas Colony, along with other audio recordings, evokes this conclusion.
Dani alludes to it when infected by a Biophage leech and complains of something being in her head. An Arcas security officer Ji-Kwan Park and inmate, Edward Bates share similar experiences, with the latter complaining he can hear something in his head. Dr. Mahler explains to Jacob that Subject Zero had the ability to control the Biophage, which can mean all those affected by it as well.