The Journeyman Project
Agent 5 is the main protagonist of the Journeyman Project Agent 5 of the Temporal Security Annex (Agency in later games). Agent 5 lives on Caldoria, Earth's first skyborne metropolis and lives a relatively mild-mannered life as an agent tasked with keeping history from being tampered with. During this time, humanity is being invited by an alien race known as the Cyrollans to join an organization called the "Symbiotry of Peaceful Beings," an intergallactic UN of sorts.
One fateful assignment will send Agent 5 to thwart the plot of Dr. Elliot Sinclair, the scientist that invented time travel. Sinclair's distrust of the Cyrollans prompts him to send three robot assassins to important temporal events pertaining to Earth's invitation into the Symbiotry. Agent 5 travels through time to dispatch of the three assassins and returns to the present day to arrest Sinclair, who himself is in the process of assassinating the Cyrollan delegate that visits Caldoria. Agent 5 incapacitates Sinclair and is proclaimed a hero.
The Journeyman Project 2: Buried in Time
Starting six months after the events of the first game, Gage Blackwood is visited by himself from ten years in the future. Future Gage claims that someone has distorted history and framed him. Future Gage enlists Gage to travel through time to clear their name. Meanwhile, as Earth's Symbiotry induction is debated, the time travel technology in use by humanity is called into question. As a result, the Temporal Security Agency is in danger of being dismantled. Gage goes to search for clues in such places as Chateau Galliard, da Vinci's workshop, Chichen Itza, and the Farnstein Space Laboratory. It's in Farnstein's lab that Gage meets Arthur, a sentient artificial intelligence who holes up in one of the Biochips in Gage's time suit. Arthur provides Gage some historical commentary and comic relief.
The plot is found to be orchestrated by Michelle Visard, or Agent 3 of the TSA. Visard captures Gage and takes him to an abandoned missile silo. There, she details her plan: make time travel technology available for all races of the Symbiotry. While Visard finishes extracting evidence from Gage's jumpsuit, Arthur turns himself into a virus and transfers into Agent 3's jumpsuit. The two of them disappear and Gage is mind-wiped and sent back to the present.
The Journeyman Project 3: Legacy of Time
The year is now 2329. The Temporal Security Agency has effectively been shut down as the TSA commissioner attempts to appeal the order. Gage Blackwood, still haunted by the memories he doesn't have, reminisces the adventures he shared with Arthur. Meanwhile, a new temporal rip is found and Gage, with no means of stopping the incoming distortion wave, is given a prototype jumpsuit that allows the user to project holographic images of other and assume their guise. Gage is sent back to the lost city of Atlantis, days after its complete destruction. There, he finds Agent 3's missing jumpsuit with Arthur still inside but no Agent 3. At the insistance of a recorded message by Agent 3 and after poking around a bit, Gage and Arthur find a code they must coordinate with codes in two other destroyed historical cities: Shangri-La and El Dorado. Upon finding the two other codes, Gage and Arthur learn of an ancient Sosiqui alien relic broken into three pieces and hidden in the ancient cities. The relic, known as the Legacy, is being fought for by the Cyrollans and another alien race known as the Quothal'as. These two alien races believe this relic to be their respective birthright. During brutal showdown in each of the time periods, all three cities are revealed to have been destroyed by the alien crossfire.
Gage and Arthur return to the three cities before their imminent destruction and infiltrate the local religious orders protecting each piece of the Legacy. With all three pieces of the Legacy returned to the present, Gage intervenes in a fight between the Cyrollans and the Quothal'as as the energy of the Legacy is channeled through him. After this, both combatants agree to a truce and to stop the fighting for rights to the Legacy. Again, for his role in utilizing time travel to save the world, Gage is commended.