It goes like this... Having time traveled the American Civil War, the Spades were stcuk downtime because of a Stopwatch-caused blackout and forced to leave their firstborn, Jonathan, with a tribe of friendly 19th-century Indians because someone may have been after them. They clocked back (well, snapped back) when Stopwatch succeeded in altering the past somehow, back to Paradise, the base at the "top" of time, but probably because he had been conceived in the past and had eaten and breathed too much past matter, Jonathan did not. Unable to retrieve him until the blackout ended, they had two other sons, Willie Jay and the youngest, Virgil, but were killed on a mission by unknown hands before they could ever retrieve him.
     He was raised by Indians until his early adulthood, when the tribe was wiped out mysteriously. Finding them dead when he returned from a lone hunting trip, he took to traveling, looking for his real family, becoming a marshall in the process. Eventually, time agents found him and brought him back to Paradise and his two brothers.
     By then, having grown up without their parents for most of their lives, the somewhat badly adapted Willie Jay had become a temporal engineer and agent and Virgil, calling himself "Ace", was a maverick time agent who didn't always like playing by the rules. Jonathan's goal thus became to reunite his family and keep his brothers out of trouble.
And then... When Simone Lorcquet came to work there, she shook things up, and not just with her karaoke singing. All three brothers found her interesting though it would be Ace who would court her more actively.
     Not that it was all fun and games! Ace had to deal with a rather nasty technician by the name of Oily Pete, and Jonathan had to contend with the intolerant head of security Vaugnharvey. And what of investor Jeremiah  Dark, a rich American who paid enough to be allowed to go on certain time trips? He knew their parents and seemed to be hiding something. It sometimes seemed like their only friends were Mission Director Thorndike, who was a friend of their parents, and young Jesse Waylons, Johnny's sf-addicted intern.
     They were never able to prove that Dark was behind the sabotage of Quebec dams supplying much-needed electricity to the base by men wearing yellow jumpsuits, and when the power ran too low, the brothers were stuck (not all voluntarily) downtime in a Comanche village (naturally Johnny's field of expertise).
     A few Native games later, and they were allowed safe passage to a nearby town, as well as a shield made from the pages of a Bible and a dagger with a strange (non-period) inscription. This clue leads the brothers on a quest to find its owner, a Stopwatch agent who may have brought something dangerous to the past. But before they follow up on it, the Comanche that helped them, now attack the frontier town because they've fallen victim to a disease apparently passed on by the brothers (though they had been decontaminated before going downtime). The town is defended, and in the process, Ace makes friends with one of Oily Pete's men, sympathetic Jimmy "Da Gun", sent downtime when the power is restored to help them.
     Now following their leads, they ride to various towns, all the while disturbed by dreams of wolves come to revenge themselves on the owners of weapons used to kill Comanche. Ace's reputation will be helped a great deal when they find the agent's canister of chemicals in a cemetery where a future land development would be, and destroy its focal referent (it snaps back to the Hive).
     On this trip they meet Lupita, an explosives smuggler Johnny wants to bring to justice (he was a marshal until recently), but she gets away (without her merchandise). Willie Jay seems interested in her, but he kinda smells, you know?
     Clocking back home, Ace is prepared to be sent downime to a 1950s drag race where his team will have to make sure no one important dies, and then another dam is sabotaged, delaying the mission. Johnny drives out to stop them and he rams right into a tree and isn't able to help. Deep questions as to the effects of this first Shift are explored, but Project doctors think it's a simple form of timesickness. Investigations into the sabotage raids turn up nothing even with the help of Matante, Johnny's historical archives contact, a woman fascinated with the time period he grew up in.
     When asked to lose the race by Oily Pete, Ace refuses, but still gets his ass kicked by mystery driver Lupita, who now appears to be a Stopwatch agent also traveling in time. The duel will end in a fireball when a car crashes into the crowd, gravely injuring team observers Simone and killing Dark, though he is cloned quickly enough. The brothers visit Simone in the infirmiry and again mystified by the last Shift, the brothers try to collect their wits before they are sent on an expedition into prehistory to investigate the deaths of 2 agents. Before they go, they find a clue to the identity of the saboteurs - a piece of yellow fabric INSIDE Paradise, near Dark's guest quarters...?
     In the past, the brothers come across a wounded giant sloth (megatherium) that attacks them, which they drive away. Following its steps leads to a cave where the agents had been feeding 21st-century food to a prehistoric horse (equus) since its birth  to eventually bring it back, but they were killed by the sloth. As they clock back with the equus, they are told the old west is once again off-limits because the (sick) Comanche they met on a previous mission have been all killed by Stopwatch.
     Soon after their return, the brothers are sent back in time to the ice age with Dark as observer to see how Neanderthals became extinct.
     They find Stopwatch agents there exterminating a tribe! They also discover that they are working with Dark, who is Stopwatch agent of some kind. They save the tribe, but also confront Dark, who shows his hand by admiting he killed their parents, as well as hinting that he too, shifts. The confrontation turns violent as Dark squares off against the brothers downtime. The Caves at Lascaux are badly damaged in the battle (soon causing a blackout at this juncture in time), and then Dark is finally killed. His body disappears, but does not reappear in the time tunnel. If he clocked back to the Hive, how could he ever have existed uptime in Project Paradise's Absolute Now?
     Through this encounter, Paradise gets wind of a secret Stopwatch operation to kidnap hotel patrons in 18th-century Paris that were important to history. Investigating, Johnny is kidnapped as well. He's rescued, of course, and Paradise approves an operation further downtime to set a trap for Stopwatch. It works, and in the new history, only Paradise agents were captured and all are able to clock back.
     The damage to the timeline of the last few days leads to a court-martial (of course called by Vaughnharvey) in which Oily Pete tries to frame the brothers. Ace proves him a Stopwatch mole instead and kills him during an oily escape (he does not disappear). The other fallout from this is that Willie Jay is offered a research position at Acheron, a base built downtime at the "bottom" of history to study primeval Earth to further keep him out of trouble (outside his brothers' influence). He leaves through  the tunnel for a new world, but leaves his brothers their parents' journal, in which they find mentions of possible shifting on their parts too, as well as examples of a strange language that never changes from shift to shift.
     Attending Oily Pete's funeral, Ace is challenged to a fight by Pete's brother, another technician called Greasy Gil. It will end badly for Gil, who gets his ear pounded and is put on medical leave and reprimand. Meanwhile, Ace can't see Simone because her father, Administrator Horace Lorcquet, has been transferred from another base and doesn't approve of their relationship. 
     On a rare time outing, Thornedike is murdered (his body snapping back) and Vaughnharvey asks the brothers for help in the investigation. They find that he didn't want to do business with dangerous supporters of the Boer war (where he had gone), and they had him killed. Johnny and Ace eventually stop a plot by these extremist Stopwatch agents to destroy London with an atomic bomb, which blows more or less harmlessly in the Thames. Greasy Gil returns briefly during this episode, with an earpiece, and his need for revenge on Ace makes him too dangerous. He's kicked off the Project permanently.
     As Horace Lorcquet assumes control of Project Paradise, putting the brothers' jobs in jeopardy, they have a linguist, Bartleby, investigate the strange script in their parents' journal. He makes headway by visiting ancient Greece, but the journal is stolen by Socrates, the philosopher (and strangely does not snap back to the Absolute Now). Confronting this Socrates, they discover he's a sophisticated artificial man (far beyond the technical ability of either Paradise or Stopwatch).
     When they bring the computer brain that was at his core to Bartleby, it gives him they key to the alien alphabet - it's Atlantean! Johnny then has Matante call on retired super-agent Manse Everard who helps convince the Project to mount a mission to ancient Atlantis, still unproven to exist. They are all captured there, and the brothers, referred to by the Atlanteans as "shifters" are thrown into a different cell... with a man called Twelve. [Click here for Twelve's history]
     They discover that Twelve is a shifter too, and while they compare notes, Everard breaks them out. In getting outside the Atlanteans' no-return field, they discover that they seem not only to know about the Shifts, but may be able to control or at least initiate them. They manage to reach the perimeter and snap uptime despite Atlantean guards running after them with laser weapons. When they reach Paradise, they are told by Manse Everard that any debt owed to Matante is wiped clean. The base is in mourning, however for the loss of Simone. A mission to medieval Scandinavia has gone wrong and she may have been captured by Stopwatch agents. Mad with love, Ace goes after her, and with the help of Johnny and Twelve, reaches the secret lair of ancient mountain people, barbarians if you will. They don't seem to work for Stopwatch.
     They only want Simone to sing a fertility song or they will attack the village where she was taken to take what they need, so after a game of King-board won by Ace, a deal is made with the barbarians that the village will send someone to sing every 10 years. Clocking back as heroes (for additionally fostering peace in time, and raising Paradise's relative probability by several % points), the mission director warms up to the brothers, and even offers Twelve a position despite being an ESPer, something not quite legal or understood.
     That order is contested by Vaughnharvey before the temporal committee, but it is finally obeyed, though a vision Twelve has of a sinking cruiseship makes the Project wary and start to investigate possible penetrations during the Titanic's fateful voyage. SHIFT>
Recently... Materializing in the time tunnel, after some further observation in the Viking settlement (to make sure Stopwatch doesn't reverse the changes), the group is sent on a mission to prevent Stopwatch from changing history by either saving or letting die key individuals on the Titanic. They are successful and continue to rise in the ranks as Time Agents. Young Jessee Waylons even graduate to full agent. But while Jonathan and Twelve are on a mission with the kid in Ancient Egypt, the "benched" Ace gets wind that Willy Jay is no longer sending his reports from the Mid-Permian Period. He undertakes a rescue mission alone and finds his brother in a tank of amniotic fluid. In the shadows, Jeremiah Dark lurks, alive and well somehow, and he's stolen something from Willie. Some kind of shimmering particles extracted from his body! In pursuit, the two Spades are distracted by a grouchy dimetrodon while Dark, evidently working with Stopwatch, clocks out.
     When the boys try to clock back to Paradise, SHIFT>
Shiftworld and all materials pertaining TM Michel M. Albert. GURPS TM Steve Jackson Games.