As a spreadeagled field approaches the final fence of the climactic pool stage, any one of six teams could come through the fog of confusion and gallop straight into the last two berths reserved for the best runners-up.
In the best of all Irish worlds, Munster and Leinster will join Ulster in a repeat of last season's treble from the RaboDirect PRO12.
Montpellier, of course, will hope to lob a large spanner into the works. They will clinch one of the last two places if they make home advantage count and defeat Toulon, already safely through.
Toulouse will join them if they win at Leicester, a classic winner-take-all which could just as easily leave the four-time European champions frozen out of the last eight and seeking refuge in the Amlin Cup.
The Tigers, still alive if only because Ospreys fly half Dan Biggar bounced three penalties off various parts of the woodwork during last Sunday's gripping 15-15 draw in Swansea, are, like Munster, happy to be finishing up at home.
Unlike Munster, the English club know precisely what they have to do.
A win of any description puts them through, unless, of course, Toulouse contrive the fiendishly difficult double of scoring four tries while also managing to lose by fewer than seven points.
Stranger things must have happened and in that highly improbable event, Toulouse would probably win the pool on 20 points by virtue of their combined results against Leicester whom they beat 23-6 in France in the autumn.
The Tigers have an enviable track record for winning the big ones while Toulouse's recent performances on the road support the theory that they are not the team they used to be.
Four successive away matches, at the Ospreys, Grenoble, Castres and Mont-de-Marsan, brought them the sum total of one try - from veteran player-coach William Servat.
Munster will be done and dusted before the Anglo-French rivals have finished revving themselves up for the last decisive fixture of the six-round pool competition.
Of all the plots and sub-plots, the most intriguing one revolves around the possibility of the last place coming down to a straight fight between Munster and Leinster.
The holders break new ground against Exeter Chiefs, one of the inspiring success stories of the English game who gave Leinster a serious run for their money at the RDS last October before succumbing 9-6 to three Jonny Sexton penalties.
Leinster know that a four-point win at Sandy Park is unlikely to be enough.
Clermont, surely the form team of the tournament whose streak of 11 wins in 12 matches is even better than Ulster's, took all five points from their trip to Devon, no mean feat considering that Saracens and Harlequins have both lost there this season.
Teams from different pools finishing on the same number of points are separated by try count and Leinster, despite more than doubling their overall tally by seeing the Scarlets off last weekend, have fewer than the majority of the rest.
The champions have managed eight, Munster nine. By Sunday lunchtime in Limerick with Racing Metro in town, director of coaching Rob Penney will have a clearer idea of how the land lies.
Munster may have missed a bonus-point trick against Edinburgh at Murrayfield but they are still in with a chance, unlike Racing who finished up being bombarded into submission by Owen Farrell's ten penalties before 35,000 in Nantes.
Ulster famously won at Thomond in the quarter-final last year but Munster's record there is still more than formidable.
Over the last ten years they have played some 30 pool matches there, winning the lot except for one - Leicester 13-6 in January 2007.
Then defending champions, Munster had qualified for the last eight before that match, just as they have qualified in 13 of the last 14 seasons.
Current last eight standings:
1 Harlequins 24 pts (27 tries)
2 Toulon 23 pts (23 tries)
3 Clermont Auvergne 23 pts (19 tries)
4 Ulster 19 pts (12 tries)
5 Toulouse 18 pts (14 tries)
6 Saracens 18 pts (10 tries)
7 Montpellier 18 pts (15 tries)
8 Leicester Tigers 16 pts (13 tries)
Others in contention for the quarter-finals as best runners-up:
Munster 15 pts (9 tries), Leinster 15 pts (8 tries), Biarritz 14 pts (14 tries), Northampton 14 pts (6 tries).
Weekend fixtures involving the above:
Friday:
Biarritz v Harlequins
Saturday:
Castres v Ulster
Exeter v Leinster
Scarlets v Clermont
Glasgow v Northampton
Montpellier v Toulon
Sunday:
Munster v Racing
Saracens v Edinburgh
Leicester v Toulouse
There is, they say, no substitute for experience. It certainly applies to European rugby where the registered list of players includes enough of the over-30 brigade to pick three Golden Oldies XVs, one for each of the three Leagues. Here goes:
RaboDirect PRO12:
Brendan Williams (Treviso - 34); Doug Howell (Munster - 34), Brian O'Driscoll (Leinster - 34*), Paddy Wallace (Ulster - 33), Sean Lamont (Glasgow - 32); Ronan O'Gara (Munster - 35), Peter Stringer (Munster - 35); Alan Jacobsen (Edinburgh - 34), Adrian Flavin (Connacht - 33), Mike Ross (Leinster - 33); Leo Cullen (Leinster - 35), Michael Swift (Connacht - 35); Ryan Jones (Ospreys - 31), Mauro Bergamasco (Zebre - 33), Joe Bearman (Ospreys - 33)
Premiership:
Geordan Murphy (Leicester - 34); Scott Hamilton (Leicester - 32), Mike Tindall (Gloucester - 34), Tom May (Northampton - 33), Mark Cueto (Sale Sharks - 33); Stephen Jones (Wasps - 35), Neil de Kock (Saracens - 34); Boris Stankovich (Leicester - 33), John Smit (Saracens - 34), Carlos Nieto (Saracens - 36); Will James (Gloucester - 36), Craig Gillies (Worcester - 36); Peter Buxton (Gloucester - 34), Neil Best (Worcester - 33), Nick Easter (Harlequins - 34)
French Top 14:
Iain Balshaw (Biarritz - 33); Paul Sackey (Stade Francais - 33), Yannick Jauzion (Toulouse - 34), Damien Traille (Biarritz - 33), Sereli Bobo (Racing - 37*); Jonny Wilkinson (Toulon - 33), Jerome Fillol (Stade Francais - 34); Michael Coetzee (Castres - 33), Sebastien Bruno (Toulon - 38), Stan Wright (Stade Francais - 34); Simon Shaw (Toulon - 39), Scott Murray (Mont-de-Marsan - 37); Julien Bonnaire (Clermont - 34), Chris Masoe (Toulon - 33), Henry Tuilagi (Perpignan - 36)
(* denotes birthdays later this month)
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