To quote from the ofFicial World Cup site Ireland's Hopes
McCarthy's dream result would be for either Cameroon to beat Germany or vice versa.
However a 0-0 draw would see both climb to five points and should Ireland only get a 1-0 win then they would face off against the Africans in a drawing of lots to see who progresses.
They would both have scored the same amount of goals, have the same goal difference and drawn their head to head match.
It would be the most painful World Cup exit since the Dutch went out on penalties to Brazil in the 1998 semi-finals and England to Argentina the same year.