Ireland will face the most daunting task in world rugby when they tackle RBS 6 Nations Championship rivals England at Twickenham on Saturday.
The Irish mission is tough enough, given England's world champion status and a ten-match winning run stretching back to last summer.
But England are also back on home soil for the first time in a Test match since last November's stunning World Cup triumph Down Under.
And losing at Twickenham is not something they experience too often.
It hasn't happened in international rugby since the 1999 World Cup, when an Andrew Mehrtens-inspired New Zealand triumphed 30-16.
Since then, England have gone 22 Tests unbeaten, while their last home defeat in Five or Six Nations rugby was so long ago - 1997 - that Britain had a Conservative Government.
No-one doubts that Ireland will provide the stiffest examination of England's RBS 6 Nations campaign, and red rose supremo Sir Clive Woodward has conceded that his players must step up a gear following away victories over Italy and Scotland.
The Irish, with centre genius Brian O'Driscoll now fully recovered from injury, and a pack that steam-rollered Wales into submission last time out, are good enough to push England hard.
But Woodward and company like nothing more than a challenge, and it would be no surprise if England produced their best display for several months.
A Twickenham full house will demand it, and England have a tendency to deliver when it really matters.