Nick Easter says Harlequins have it in them to shatter Saracens' hopes of the double, despite the drubbing they took at the hands of their north London rivals six weeks ago.
And the no8 says that if they manage it, and go on to beat Leicester or Northampton in the Aviva Premiership final at Twickenham on May 31, it will rank as the club's greatest achievement.
Sarries have been the team of the season – striding to the top of the table in the regular season and turning in a monumental world-class performance against Clermont Auvergne to reach next week's Heineken Cup final.
Quins themselves have been on the receiving end of that awesome power. They were outgunned 39-17 when the sides met at Wembley in March.
But that was before Easter and his men went on their great late charge into the play-offs and the former England number eight is convinced an upset is on the cards.
“It's a huge challenge, we know that,” said Easter, who will set a new club appearance record of 233 games when the sides go head-to-head at Allianz Park tomorrow (Saturday).
“They've walked away with the regular league and their form in Europe's been unstoppable.
“They are in good form and we know we've got to be on the money. We don't have a good record against them, but we'll give it our all.
“No-one's unbeatable. I've been around long enough to know that on any given day, if you perform, anything can happen. We will have a plan, it's just about executing it.”
Looking back at that defeat at Wembley, Easter said: “We gifted them the first four tries and the game was over.
“We actually did some good stuff at Wembley and scored two good tries, but you have to be accurate. You can't feed them anything. It will be about keeping the ball and accuracy.
“You can't be cagey against a team like Saracens either, because it plays into their hands.
"And they've shown that once they get ahead, they are a very difficult side, with their blitz defence and their kick-chase game. You have to get ahead of them to try and free the game up.”
Easter added: “It would be our greatest achievement to win this year's Aviva Premiership title, but it's a long way off. It's two of the toughest games of the season.
“We've had a lot of knock-backs. Up to six weeks ago we weren't able to pick the same team twice, given the injury situation we had and the league position we were in.
“But since that Sarries game, it's been literally 'we have to win these next five games', which we've managed to do and we have momentum.”