McGrath hoping to kick ahead after his 'spot-on' cameo against England
There are two minutes left in Ireland's season and nobody knows which way the ball will bounce.
England trail by a score and are menacing, desperately defying their weakening grip on a back-to-back Grand Slam with a stirring recovery off the ropes.
Ireland have the ball though, beyond halfway, tentatively tip-toeing through the trenches. As a ruck forms, Ireland's third-choice scrum-half skates towards its base.
He has already eyed a patch of grass in the right corner; he taps Iain Henderson knowingly as he enters; Henderson moves aside; behind him, so too does Cian Healy, expecting a pass behind for a dropped goal attempt.
Luke McGrath is seizing this moment, one so close to that of triumph, all for himself though. Having taken a second look, he picks and kicks; the ball lands behind Jack Nowell, in the exact spot of grass which had been investigated seconds earlier.
The ball bounces gleefully across the touchline into the safety of the crowd who now know that they do not have long to wait for victory to be confirmed thanks to the precision of a precocious Championship debutant.
Cheered These are the days when you learn how to fly.
"It was not just tactically sound," marvelled Joe Schmidt as the crowds still cheered, "but huge courage-wise, and then technically to get that close to the corner was spot-on."
Even a month later, McGrath also appreciates the significance of that intervention.
"It was an incredible moment in my career and those moments give you a bit more confidence," he says. "It just boosts your confidence a bit more and I'm trying to bring that back into Leinster.
"And I feel I have done that in the last few games but I also feel that there's a lot more that I can improve on still.
"The atmosphere in the last 10 minutes was something I'd never experienced before."
It aided his further excellence against Wasps weeks later, and will do so again when Leinster enter a Lyon bear-pit to tackle Clermont and their irrepressible petit general, Morgan Parra.
"He's incredibly talented. I watched him growing up, he's exciting. He's their talisman, he brings their pace when they want to play quick, his kicking game, everything really."
Nerves naturally obtained, but didn't restrain, against England. Their return will paradoxically comfort him this weekend. "When I was coming on against England, yeah very nervous. I think you were always going to be. I was very nervous but the experience around me helped me move on.
"I don't get sick fortunately. But it's kind of funny, the thoughts are going through your head.
"But when you're on the pitch, it's one job at a time. There is no point in thinking, is it coming down to this or that. It's got to be one phase at a time."
And being decisive, as Leinster have declared they will be from the off, will help too.
"Going over to France, you know how loud it's going to be. It's such a challenge, their attack speaks for itself.
"They're lifted by the crowd. We're going to have to work incredibly hard for each other. They convert a lot of their line-breaks.
"If that happens, we're going to have to work incredibly hard for each other to get back. We need to impose our game.
"We want speed of ball, we have to try and run the bigger packs around.
"What's been going well for us has been our unstructured attack and last week our defence was good too.
"Connacht played a really good attacking shape which was brilliant for us to get that kind of game in before we go over to France.
"We know we have to go for it, especially the way they play on home soil."