Only a handful of Formula 1 world champions have been as closely identified with a single team as Lewis Hamilton was with McLaren, yet this year the Briton announced that he was bidding farewell to the squad that had nurtured him since childhood to take on a new challenge at so-far-unsuccessful Mercedes.
Suddenly what had been a frozen driver market was unlocked. McLaren instantly picked Sergio Perez as Hamilton's successor - then saw the Mexican's season nosedive.
Hamilton's arrival at Mercedes backed Michael Schumacher into a corner where retirement was the only palatable option. And somehow, amid it all, Felipe Massa kept a Ferrari seat he had seemed certain to lose...
Early in the year, Hamilton looked set for a mere cameo role in the silly season. Yes, his McLaren contract was up for renewal. But few seriously imagined he would leave, despite the previous summer's public flirtation with Red Bull and comments about the importance of keeping his trophies despite McLaren's policy on the issue.
It was only after the summer break that a Hamilton move seemed to be a realistic possibility. The spat caused by a disgruntled Hamilton tweeting set-up data at Spa lifted the lid on some of the tensions in the driver/team dynamic, and even as McLaren hit briefly dominant form, a Mercedes switch seemed ever more likely.
Then, days after he had retired from a dominant Singapore lead, it became official: Hamilton was off.
He insisted he was under no illusions about Mercedes' form, but was excited by the prospect of turning it into a winner. Whether he succeeds or fails, Hamilton has certainly started a fascinating new story.
McLaren had previously intimated that it was so confident of retaining Hamilton that contingency plans were not on the agenda. But soon it would need one.
Although F1 was spoilt for rising stars in 2012, all had question marks over them - and eventual McLaren choice Perez was no exception.
His drives to the Sepang, Montreal and Monza podiums were extraordinary, but were they tyre flukes? And was Sauber team-mate Kamui Kobayashi's superior qualifying record telling? Why was Ferrari, which had nurtured him so far, so reluctant to give him a chance?
When Perez's points dried up and his mistakes multiplied in the races following his McLaren deal, critics were quick to laugh in McLaren's direction. Nico Hulkenberg's superb end to 2012 didn't help, Force India's German making a belated case that he was the young gun truly most deserving of a big break.
Perez and McLaren were undaunted. The team insisted it was just a case of rough edges to round off. Perez urged sceptics to judge him in 2013.
The saga of whether Schumacher would extend his F1 comeback beyond his initial three-year Mercedes deal had been rumbling along pretty much from the day he got back into silver overalls.
It was as tough to judge as ever in early-2012. He seemed closer on pace to team-mate Nico Rosberg than before, but the mistakes weren't going away, and they no longer seemed uncharacteristic. Woeful reliability on his car didn't help.
As Schumacher postponed his decision through the summer, Mercedes made the first move. Few thought the German firm would be brave enough to oust the nation's greatest motorsport hero before he was ready, but signing Hamilton had exactly that effect. After brief rumours of a Sauber deal and a lot of talk (none from Schumacher) of racing elsewhere, his second retirement was confirmed.
When he first started in F1, Hamilton had often spoken of his regret that Schumacher had retired just before they had chance to face each other. Now they had done so, but it hadn't been the great confrontation it once would have been. And now it was Hamilton holding the exit door open for the seven-time world champion...