"What about you Harper? What do you think went wrong?"
Harper raised his head, and with barely a pause for breath, chirped: "I don't think the tactics worked."
He and his team-mates braced themselves for the nuclear reaction that has since become legendary, only to find that none was forthcoming, at least not until training was over. That was when Harper was called into Ferguson's office, and given the mother of all dressing-downs. "Who do you think you are to question my tactics?" bellowed the manager, jabbing his finger ever further into the striker's face.
At which point, Harper committed his second sin of the day, swiping away the offending digit, and heading for the door. "I'm not paid to manage the club, but you asked for my opinion and I gave an honest answer," was his parting shot. "If you don't want my opinion, don't ask for it."
Not only did their relationship fail to recover, it deteriorated, and has continued to do so since, this month reaching a new low with the publication of Harper's autobiography. In King Joey: Up Front And Personal, Aberdeen's all-time top scorer, with 205 goals spanning two spells at the club, allows himself to exact a measure of revenge on the man who wanted him out of Pittodrie from the moment he arrived in 1978.
Harper, now 60, scored 32 goals in Ferguson's first season, but found himself dropped towards the end of it. Having missed much of the following campaign through injury, he says he had to beg for the league championship medal he was entitled to. His departure the following May, at the age of 33, was inevitable, but the way it was handled reduced him to tears. "I don't want to see you here ever again," said Ferguson.
In his 1999 autobiography, the man who went on to conquer Europe with Manchester United refers to Harper as an "artful dodger", who tried to flatter him in the interests of securing a lucrative testimonial. He describes him as "the only individual who represented a long-term problem" at Aberdeen, a player he found himself lapping on endurance runs. Ferguson, who preferred the industry of Mark McGhee and Steve Archibald, added that Aberdeen would not have won the league had Harper avoided injury.
Harper has never been one to take criticism lightly. When a drunk journalist goaded his team-mate, Arthur Graham, he silenced him with a right hook. When he was carried off with a serious knee injury at Celtic Park, to the strains of "Harper's a barrel, Harper's a barrel of shite," he sat up on his stretcher to blow them kisses. So it's no surprise to find in his book a denial of Ferguson's claims, and a character assassination of his own, which he is more than happy to discuss.
"I know they all hail him as a great man, but in those days he wasn't so great. He was only about six years older than me, but there he was, sticking his finger in my face. I wasn't going to stand for it. He was not a nice person to me. A lot of people in Aberdeen think the sun shines out of his behind, but they are not mates, they are hangers-on."
Harper says he upstaged Ferguson as a player, most notably on the SFA's summer tour of 1967, and wonders if that is the source of his resentment. He also suspects that the manager felt threatened by the striker's popularity, sky high since 1970, when his goal helped Aberdeen to win only their second Scottish Cup. "If you look at Fergie's career since he left Aberdeen, he got rid of Beckham, Keane, Van Nistelrooy, guys who were popular. There is obviously something he doesn't like about that.
"He's a multi-millionaire, and he's brought out books slaughtering people. Gordon Strachan, Jim Leighton, you name it. How much money does the guy need to slag people who got him where he is? He was a very, very mediocre player. Obviously, he has become a very good manager, but he is also very lucky. He got sacked by St Mirren. He did remarkably well at Aberdeen, but he was one game away from getting sacked by Manchester United. Even in the European Cup final, when they beat Bayern Munich, they scored two goals in the last minute. You need that luck."
When a managerial vacancy arose at Arbroath, Harper called up his old boss, and asked if he could put a word in. "He said no, and put the phone down," recalls Harper. "I don't know why I did it. I knew he wouldn't help, but my wife talked me into it."
Harper, of course, is no angel. The son of a shipyard worker in Greenock, he spent his boyhood years clambering into Cappielow without paying. A self confessed jack the lad, the player who started his career with Morton hid in the bushes during training runs, drank a lot ("although not after Wednesday"), and was once compared to a Toby jug by Ally MacLeod. None of which appealed to supporters of Hibs, where his two-year stint coincided with the disintegration of Turnbull's Tornadoes. Harper scored five in a friendly against Nijmegen, and was booed off the pitch.
But his flaws were also his forte. An instinctive player, he believed that the brain was quicker than the feet, that his meaty thighs need only be used to feed on scraps in and around the box. A bit of a chancer, he used to grab defenders by the testicles to gain half a yard, but it worked, and the Aberdeen fans loved it. He was one of them. By sliding to his knees after every goal, he became King of the Beach End, a wee man they idolised, not just for scoring a penalty at Hampden in 1970, but for his pre-amble to it. During a nine-minute delay in which Celtic's players protested to the referee, Harper was playing keepy-uppy on the spot.
His Scotland debut, against Denmark in 1972, was no less entertaining. Although listed as a substitute by Tommy Docherty, he had been told that he wouldn't play, so when the manager looked along the touchline with 30 minutes left and told him to get stripped, he wasn't ready. "But boss, I need to pee," said Harper, who disappeared up the tunnel in search of a toilet. Lost in the corridors of a foreign stadium, he opened the wrong door, and closed it behind him, only to find that he was out in the street. He quickly relieved himself, scuttled along to the main entrance, and after persuading a sceptical receptionist that he played for Scotland, scored in a 4-1 victory.
Remarkably, that first appearance came only after he had left Aberdeen for Everton. The previous season, his 31 goals, 52 in all competitions, made him Europe's third-top scorer, the reward for which was a bronze boot. "It took me a long time to break into the Scotland team because in those days Rangers and Celtic players always got in ahead of you. For three seasons, I was top goalscorer in Scotland, but never got a chance to play for my country. As soon as I moved to Everton, I got a cap."
Harper, who returned to Aberdeen via Hibs, only made four Scotland appearances in all, the last of which was against Iran in the 1978 World Cup. He has few fond memories of Argentina, what with the early exit, the Willie Johnston drugs scandal and a team hotel that slept three to a room. Harper lay between Alan Rough and Derek Johnstone, which he describes as "a nightly trial". Both were naked save for their perms, only the colour of which varied as he turned this way and that.
It might have been worse still had they undertaken the drugs test that did for Johnston. One day, when the SFA doctor visited their room, he spotted a nasal spray that all three had been using. "What the f**k is that doing there?" he screamed, before explaining that elements of it were on the banned list. "We were only using it to clear our passages," says Harper. "But if someone had tested us after training, we could have been done too."
He blames his flimsy international career on the "Rangers-Celtic syndrome", and the life ban he was handed in 1975. Part of the so-called Copenhagen Five, who were involved in a nightclub disturbance after another match against Denmark, he and Arthur Graham have always denied that they were anything more than innocent bystanders, but the SFA would not allow them to make their case. "I was disgusted with the SFA," he says. "And I'm still bitter about it now. I really did think about chucking football."
Harper contemplated taking the matter to court, until he received a late night phone call from a senior SFA source. "I wish I'd had a tape recorder. He said they knew that Arthur and I hadn't done anything, but for the good of Scottish football, the ban still stood. If I took the matter further, I would never play for Scotland again. If I didn't, I could be back within a year. Thirteen months later, I was playing in the World Cup."
It was one of the few occasions in Harper's life when he was not permitted the last word. Even now, he is quick to voice his opinions on the radio and in the local newspaper, but he has cut back his commitments to the after-dinner circuit since suffering a stroke in 2004. He doesn't know what the future holds for his beloved Aberdeen, where he can still be found greeting guests on match days. "But I know one thing for sure," he says. "I will go to my grave knowing that I'm their top goalscorer, and I'll never be beaten."
King Joey: Up Front And Personal (Birlinn, 16.99).