RIGHT now it feels like all of Aberdeen is perched at the edge of a high-diving board.

This could go one of two ways: either this new Pittodrie team emerging under Derek McInnes is about to make a great jump forward, or else it is going to drop into a painful descent. The League Cup semi-final against St Johnstone does not allow for any shades of grey. Six months into their season and Aberdeen have come to crossroads.

More than 12,000 supporters will mobilise to fill three-quarters of Tynecastle. It is a support that has been through the mill over the years given the litany of cup debacles various teams and managers have inflicted on them. The headline disgrace is not even that the club with the third or fourth best resources in the country has not made it to a cup final for 14 years; it is that most of the time even getting to semi-finals has been beyond them.

Tomorrow will be only the sixth they have contested in 27 attempts since reaching the 2000 Scottish Cup final. The aggregate score from those previous five? Predictably dire: scored six, conceded 18.

The last time Aberdeen got through a semi-final McInnes was 28 years old. The club captain, grizzled veteran Russell Anderson, was 21. Peter Pawlett was nine, for heaven's sake. One of the big tests for McInnes since his team beat Motherwell in the quarter-final way back in October has been maintaining equilibrium around Pittodrie. For years Aberdeen have come within touching distance of something, built some momentum ahead of some significant hurdle, only to collapse in an almighty letdown.

That is partly why McInnes has chosen his words with the precision of a surgeon in the long build-up to Tynecastle. But supporters also know this much: this team looks to be coming together as Aberdeen's best for a number of seasons. They are second in the SPFL Premiership, two places and 12 points better off than at the same last season, and playing with aggression, vigour and character. And then there is the broader landscape of the League Cup: the bookmakers, and plenty of others besides, expect Aberdeen to beat St Johnstone and then either Hearts or Inverness Caledonian Thistle in the final (even though those two have posted three wins over Aberdeen since the campaign began).

Aberdeen's tendency to lose semi-finals is shared by McInnes himself, who reached two as a player and three as a manager at St Johnstone without being on the winning side. "Everybody wants to be part of that big day in the final. What has to be remembered is that three of the St Johnstone semi-finals came as a first division club. Two for me came as player. Apart from against Motherwell, we lost to the team that won the cup. We had done really well as a team to get that far. I do feel I have to make that point.

"People ask me about previous disappointments for the club but for me it's the same as the previous successes at Aberdeen: it's not relevant for this team. For this team and for myself it's our first semi-final at the first time of asking. We're in it, it's up to us to make the most of it now.

"Having a huge support behind us brings a pressure but comes with it, that's part of the deal when you sign up for Aberdeen. You know that the support's there. They have given us great backing all season, they have come in big numbers and they have snapped up the tickets for Saturday. That's brilliant to see."

McInnes is not the type to allow the semi-final build up to become suffocating but there was an escape for him yesterday as he busied himself in reshaping his squad. Shaleum Logan arrived from Brentford, while Josh Magennis was loaned to St Mirren and Chris Clark was released.

Logan can play in midfield or at left-back but the 26-year-old is most at home as a right-back and will be predominantly used there by McInnes. Logan began his career with Manchester City before a few loan spells and then a move to Brentford in 2001. Joe Shaughnessy's League Cup suspension should mean an immediate debut for Logan tomorrow.

"Once we were aware that Shaleum was maybe available for loan we went out of our way to get him," said the Aberdeen manager. "He offers good pace, good energy, good athleticism, he's a good one-v-one defender. We are hoping that he buys into what we are trying to do this season." Logan himself told the club's website that supporters could expect "an attacking full-back".

His arrival will be the last at Pittodrie in this window and, for all that the squad has needed a dedicated full-back, the new signing which really caught the imagination was Adam Rooney. Ask McInnes what he likes about the Irishman and he reels off a list including his unselfish runs, the questions he asks of centre-halves, his anticipation, his movement and his finishing. "He looks like an Aberdeen player."

Tynecastle will reveal whether that is beginning to mean something different than it has for the last 14 years.