In every sporting competition there is a defining moment when the tournament gets serious. Golf has "moving day," football has "squeaky bum time" and the Heineken Cup has the back-to-back double headers.
The tournament won't be won in the coming weekends but these 24 games will go a long way to shaping the final standings.
Some teams are entering the last-chance saloon, while others will be looking to kick on after bright starts to their campaigns.
Here is a run down of all the upcoming fixtures and a prediction of the results.
Munster vs. Saracens
It could be argued that the legend of the modern Munster was born in two games against Saracens way back in 2000. The two sides shared 130 points over the games, with Munster prevailing by a single point on each occasion, scoring at the death in both matches.
Saracens will return to Limerick looking to land the punch that could sound the death knell for a once great Munster side, one that has been faltering in recent years.
If any side is built to conquer fortress Thomand Park, it is Sarries. They have a pack that will not be intimidated and a kicker that will punish any indiscretions. They won't be fazed by the atmosphere and will try to impose their game on Munster.
Their English contingent will have been buoyed by last weekend's defeat of New Zealand, and that should boost the whole squad.
Munster, on the other hand, are in the process of rebuilding under new coach Rob Penney. The signs have been positive but they have a long way to go, and will enter the game with a growing injury list.
They aren't the Munster of old, but won't go down without a fight.
Prediction: Munster by less than seven points with no try bonus point.
Racing Metro vs. Edinburgh
All the focus has been on the Munster/Saracens game, but this game will be no less important to the group's final makeup.
The French are notoriously ambivalent when it comes to the Heineken Cup. As soon as their chances seem over, they tend to turn their attention elsewhere.
Racing Metro will come into this game chasing a bonus-point victory, anything less could lead to them focusing on the Top 14.
Edinburgh promised much, but have failed to build on last season's heroics. They have flattered to deceive in the Pro 12, and have failed to score a single point in their two Heineken Cup games so far.
Prediction: Racing Metro by more than seven with try bonus point.
Leicester vs. Treviso
These two sides enter this fixture with totally different priorities. Leicester are chasing maximum points, while Treviso will be out to avoid embarrassment.
Already three points of the pace set by Toulouse, Leicester need to secure maximum points to put the pressure on the Frenchmen before they travel to Leicester in the new year.
Having seen this Leicester won't take the same liberties, and should look to put the Italians away early and not leave anything up to chance.
Prediction Leicester by more than seven with a bonus point.
Toulouse vs. Ospreys
Last season's Pro 12 Champions, the Ospreys had a very poor start to the season but seem to be gaining a head of steam in recent weeks.
They will travel to France needing to secure a losing bonus point at the very least, but will hope to emulate the Scarlets and surprise Toulouse.
Toulouse shot themselves in the foot by failing to secure a bonus point in Italy. In the Heineken Cup every point counts and this could come back to haunt them.
Victory by any means will be the priority but they would love a bonus point. They will look to build an early lead and hope to rack up the tries once the game is won.
Prediction: Toulouse by more than seven with no bonus point.
Zebre vs. Harlequins
One must really worry for the plucky Italians in this fixture. Winless in 12 competitive fixtures, they welcome one of the form sides in European rugby.
Cobbled together from the ruins of Aironi, Zebre are still searching for their identity. They are a plucky unit but don't have the firepower to challenge the might of Harlequins.
Quins welcome back their Internationals and will accept nothing less than a bonus-point win. Last year's near miss means they won't take it easy on their overmatched opponents.
Prediction: Harlequins by more than seven with a bonus point.
Connacht vs. Biarritz
Galway on a wet winters night with a cold wind blowing in from the Atlantic would be enough to put off most sides, just ask Harlequins, so one must worry about the men from the South of France.
Connacht's raucous crowd are their 16th man, but the weather can be their 17th. They will try to slow this game right down and turn it into a dog-fight.
While qualification is probably out of their reach, they will be head-hunting on Friday night when they welcome Biarritz.
Biarritz are European veterans so might take the conditions in their stride, but one must question if their focus will be elsewhere given their struggles at home.
Prediction: Connacht by less than seven with no bonus point.
Northampton vs. Ulster
One of the plum ties of the round will take place in Franklin's Gardens, where the in-form Ulster will look to knock Northampton out of contention.
Ulster are yet to be taste defeat this season, capable of winning both dogfights and shootouts. Their combination of pace and power has so far been unmatched.
Their Irish contingent are all in fine form, while a host of injured stars are due to return from injury.
Northampton's defeat in France didn't end their hopes of qualification, but they are a side on the ropes. Defeat will all but end their European dream so expect them to come out swinging.
Both sides like to spread the ball so this should be an enthralling affair with lots of momentum shifts.
Prediction: Ulster by less than seven with a bonus point.
Glasgow vs. Castre
While this game might not appear important, it could have a huge bearing on the long-term hopes of both Northampton and Ulster.
Ulster will be supporting Castre, while Northampton will be hoping for a Glasgow win.
A Castre win would keep them focused on Europe and more likely to take points off Northampton in Round 5, while Glasgow's attention would be elsewhere when they travel to Ravenhill.
A Glasgow win would mean probably end Castre's aspirations in Europe and thus, they would be less likely to throw a spanner in the works when they visit Northampton.
Prediction: Castre by less than seven with no bonus point.
Clermont vs. Leinster
Leinster have been below their best this season and find themselves two points off the pace, having failed to secure any bonus points.
If they are to win the group they will need to win in France, while defeat will leave their hopes of qualification hanging by a thread.
Clermont would like nothing more than to knock Leinster out of Europe, so expect fireworks as these two heavyweights go to war.
Prediction: Clermont by less than seven with no bonus point.
Scarlets vs. Exeter
This game is nothing more than a dead rubber as, miracle aside, both sides have no choice of qualifying for the knockout stages.
The Scarlets are a talented team, but have failed to reach their potential just yet. They have too much potential to go winless and will view this game as a must-win.
Exeter don't do dead-rubbers, so expect no shortage of effort from the Englishmen. They have won lots of fans in recent years through their honesty of effort and will be hoping to spring a surprise.
Prediction: Scarlets by less than seven with no bonus point.
Sale vs. Toulon
On paper this game seems like a formality. Toulon should have way too much power for a struggling Sale outfit, but the Heineken Cup can surprise you when you least expect it.
Sale are rooted to the foot of the Aviva Premiership with just one win from 10, but there have been hints of a revival in recent weeks.
Toulon, on the other hand, have been on a tear in France, winning 10 of their 12 games, as they look to better last season's runner-up finish.
Toulon won't be worried about bonus points, looking for Jonny Wilkinson to kick them out of sight.
Prediction: Toulon by more than seven with no bonus point.
Cardiff vs. Montpellier
Cardiff have been valiant in defeat so far, but find themselves rooted to the foot of the table and in need of a big win to revitalise their season.
They are probably long shots to qualify but they won't go down without a fight, targeting this game as one of there few remaining chances to save face.
Montpellier have been a pleasant surprise in recent years, building a side with a real sense of pride and unity.
A win will keep them in the hunt to qualify as one of the best runner-ups, but defeat wouldn't be disastrous
Prediction: Cardiff by less than seven with no bonus point.