It was billed as one of those scenes from a master criminal movie.
Had Ulster finally found the code to crack open the safe place that Leinster have usually found The RDS to be in times of greatest need?
The form suggested 'Yes'; the history answered 'No'.
It was a toss of the coin all day, all the way from Belfast to Dublin.
That is what makes for the most memorable matches, the not knowing, the absence of certainty from the cheap seats, the presence of doubt on the field of play.
For once this season, the flags, blue and white, were waving with energy as the provinces entered the coliseum.
The returning Luke Fitzgerald took the first high, hanging kick from Eoin Reddan and Jonathan Sexton moved it from there to put the home side in prime position.
Leinster did what they did not do all season by making possession tell from Reddan's razor-sharp flat pass for Isa Nacewa to cut a fine line for try time.
Sexton converted from the right for the perfect start in the fifth minute.
Ruan Pienaar's kicking game was countered by Fitzgerald's chase of the high ball.
The driving of Mick Kearney caused Chris Henry to cough up a penalty for Sexton to nail one from 40 metres on the angle.
Fitzgerald flew down the left for Reddan and Sexton to orchestrate an attack bumped up by Jordi Murphy and Richardt Strauss for Sexton to make it 13-0 in the 16th minute.
It was all Leinster to this point.
The first real threat from Ulster was interrupted by Rhys Ruddock's take-down of Luke Marshall and concluded by Ben Te'o and Nacewa muscling Ian Henderson into touch.
Paddy Jackson's precision pass to Craig Gilroy was a problem soon solved. But, Luke Marshall's nifty link to Gilroy forced Reddan into emergency service.
The Ulstermen were making inroads close-in and Jackson exacted a three-point toll in the 27th minute.
When Jack McGrath was whistled for a high hit on Marshall, it ceded possession and territory.
Ulster came calling through Stuart McCloskey and Iain Henderson for Jackson to add three points for a borderline decision by referee Ian Davies on Richardt Strauss's steal at the breakdown.
Sexton's tumbling kick was a thing of beauty when most options had been exhausted. The footwork of Nacewa was combated by Ulster counter-rucking.
Leinster's healthy lead was in danger of evaporating when McCloskey careered over the gain line and Jackson fed Gilroy to resist the hit from Dave Kearney in the left corner to leave it 13-11 at the interval.
Ulster were in the driving seat.
Garry Ringrose took Jared Payne neck high and Jackson put the visitors within striking distance.
There was period of frenetic rugby that swung one way then the other as Sexton kicked away guaranteed territory from a rash penalty for Ulster to go through the gears before Jamie Heaslip earned a penalty.
From there, the big boys drove it up the guts from Devin Toner's lineout claim for Ringrose's change of direction to create the overlap converted by Te'o's offload and Heaslip's ball security over the top of Jackson.
Sexton was spot-on from the conversion for a 10-point gap in the 50th minute.
The introduction of Leinster's two-man cavalry of Tadhg Furlong and Sean Cronin made all the difference at their first scrum for Sexton to take The Blues thirteen clear.
Sexton saw the sense of keeping the pressure on. Henry knocked on. The scrum went into overdrive and, two phases on, Furlong got close and Cronin got over for Sexton's extras to make it a done deal in the 65th minute.
The activation of Gilroy from a splendid set-piece move allowed Jackson to convert.
They were still alive until Stuart Olding was seen off by Jack Conan and Luke McGrath in the corner for Leinster to take their revenge for Kingspan and make their sixth final in seven seasons.
Pro12 semi-final: Leinster 30 Ulster 18