For Norwich City fans there can be fewer low points than the day they witnessed City thrashed 7-1 on their own ground by Colchester United.

Disaster upon disaster seemed to be piling up at City's front door like unwanted junk mail and the opening day defeat of the 2009-10 season was just another piece of rubbish dumped on the doorstep. Relegation, misguided managerial appointment producing misguided transfer dealings producing players who couldn't give a monkey's chuff about Norwich City Football Club.

But far from trying to brush the Colchester game under the carpet, City fans have come to celebrate it as a turning point of almost indescribable proportions in the club's history.

It spelled the end for manager Bryan Gunn and the beginning of the Paul Lambert era. Lambert, the man who had masterminded Colchester's stunning victory.

That the relationship with him has ended after a little under three years is a cause for some concern, because Lambert will be a very hard act to follow.

How do you replace a man who picked up the team by its ears, shook it up, let the dross blow away on the wind and then turned it into one which has swept almost everything before it? His work on the field has helped transform the club off the field – debts are being managed and we can all sit a lot more easily having seen the real danger of going into administration brush past the club uncomfortably close, but failing to stop.

Lambert's impact at Carrow Road was sudden.

Gunn had survived one more game, at Yeovil in the Carling Cup, but had gone by the time City played out a dull 1-1 draw at Exeter the following weekend. Three days later, Lambert walked into the media room at Carrow Road as the club's new manager and in the evening watched City at Brentford. It was uninspiring stuff.

Lambert went to work – there was plenty to work on – and on the training fields at Colney spotted young Korey Smith going through his paces. He liked what he saw and put Smith, a bit part player having just emerged from the Academy team, into his first team. Smith was young and hungry, not without talent. He was a Norwich City player through and through and he was eager to learn. Smith put every single ounce of effort into his performances.

In a way, Korey Smith came to characterise what Lambert wanted in a player. Not for him expensive signings, full or loan, who, in his words, didn't care about the club.

Him, assistant manager Ian Culverhouse and football operations manager Gary Karsa clearly knew who they wanted – players who could do the job, players who had the ability, but just wanted to prove it. Fraser Forster was a terrific young keeper, hopeful of breaking into the Newcastle first team picture – Carrow Road was a perfect shop window.

Russell Martin had helped take Peterborough up to the Championship, but found himself unwanted at London Road – Lambert gave him a second wind, and boy did he sail into it.

Later there would be Andrew Crofts, David Fox – 'he has an annoying habit of always seeming to find a team-mate with his passes,' Lambert would say – Zak Whitbread, John Ruddy and plenty others.

What Lambert managed to do was to start ripping pieces out of City's seven-year plan. City charged up the table, overtook Charlton and Leeds, sat down on top spot and never looked anything but champions. They steam-rollered teams. The policy was: if there is a point to be won, go out and win it. City became famous for their penchant for winning games late on. They were becoming a team in the image of their manager. They were neat and tidy to look at, but had a ruthless streak underneath.

The success continued in the Championship as that plan began to look increasingly like kitty litter.

There were few disappointments, but many highs, and never has a trip down the A140 to Ipswich been enjoyed more than it was on April 21, 2011. City had already whipped their rivals 4-1 at Carrow Road in November, but as the march towards promotion gathered momentum, the trip into Suffolk was one to savour. Winning at Portman Road is always sweet – winning 5-1 was absolutely incredible. If Lambert's status at Norwich ever needed confirming, this did it. A 3-2 home win over Derby followed – although that hardly tells the story of a night when City were indebted to Simeon Jackson's second-half hat-trick, but particularly his injury-time winner.

When Cardiff lost 3-0 at home to Middlesbrough on May 2, City knew a win at Portsmouth in the evening would see them promoted – and Jackson duly came up trumps again. Promotion was sealed as runners-up.

The trick was to stay up – and City did that in impressive style.

Lambert was feted almost everywhere he went – as was his team. Finishing 12th was a superb achievement, but there was never any doubt that the success would bring its difficulties. Clubs without managers circle and in this case Aston Villa seemed to be the perfect fit: under-achievers with a desperate need for someone to do what Lambert had done at Norwich. There was clearly one man suited to the job.

We all knew Lambert would go one day – it was a case of when, not if. In recent weeks some believe they had seen little clues – hints that perhaps he wasn't getting just what he wanted at Carrow Road. There were reports that he wanted more money to strengthen his playing squad – doesn't every manager?

In the background were the managerial vacancies at Villa and Liverpool. Lambert is reluctant to discuss what MIGHT happen, no matter the subject, so the likelihood of him talking about speculation linking him with a managerial vacancy was virtually nil. He said as much in a press conference following Adam Drury's testimonial match.

His outburst was an angry one; he's had a few run-ins with the media, but the line of questioning touched a nerve. Lambert was wanted by Burnley in January, 2011, but took umbrage when questioned about it. His reasoning? That he could not make promises about the following day. Football, he suggested, was a strange animal which behaved in strange ways. He could be the victim if he lost a few games, he could be the guilty party if he won too many and walked away. It was diplomatic to steer clear of speculation about his future – even though by his very actions he actually increased it.

His departure may put an end to that on a personal level, but it will simply prompt more questions.

What of the playing staff? Who will follow him? And, most crucially of all, will the board of Norwich City Football Club be able to get it so right again when it comes to appointing a new manager?