Craig Gardner is the spy who came in from the claret and blue.
As a member of Aston Villa's squad he was a self-confessed "undercover Birmingham City fan". Now playing "the football of my life for the club of my dreams", he aims to halt Villa's run of six successive wins over their neighbours tomorrow – and give Gérard Houllier a torrid introduction to the Second City derby.
The instant effect of Alex McLeish's team breaking Villa's grip on local bragging rights, apart from piling pressure on Houllier, would be to lift them above their rivals in the Premier League. The bigger picture reveals that Birmingham have finished above Villa only once in 35 years, in 2003, but Gardner believes a shift in the balance of power may be imminent.
"We're the underdogs and Villa have been the top team for the past few years," says the 23-year-old attacking midfielder. "But last season we finished really high [ninth] and we're looking to improve on that. Villa are looking over their shoulders now – and so they should be. I'd like them to be the underdogs. It would be amazing to finish above them. Then we could give them back six or seven years of stick."
Gardner comes from a "Bluenose" family and is likely to be the only Brummie in the starting line-ups. Yet as a 19-year-old who progressed through Villa's youth system he helped them beat his boyhood favourites before defecting to St Andrew's in a £3m deal in January. Preparing to return to Villa Park, having appeared there for his new club in their contentious defeat in April, he offered a telling distinction between being thoroughly professional for Villa and a fanatic in the first team at Birmingham.
"When I was a Villa player, being an undercover Birmingham fan, it was my job. Whoever I'm playing for I'll give 110 per cent, but being a Blues fan and playing in this game, I'll give 150 per cent. It's a game I dreamed about playing in. It's massive. I'll be pinching myself in the tunnel before we go out. I'll be thinking: 'This is really happening. Come on, let's do it'.
"It's just another game for the players and the staff – we haven't changed our training regime – but for supporters it's the one they can't wait for. When the fixtures come out, they say, 'When have we got Villa?' It was the first thing I asked. Everywhere you go, you get Villa fans coming up saying, 'You're gonna get beat', and Blues fans telling you, 'Let's do it this time'."
Gardner, whose 18-year-old brother Gary is with Villa, struggled to break into Martin O'Neill's midfield but is thriving under McLeish's management, top-scoring this season with four goals despite a three-match suspension. Ironically, given the sale of James Milner, injuries to Stiliyan Petrov and Fabian Delph plus the suspension of Marc Albrighton, he might have made Houllier's 11 tomorrow. But there are "no regrets" and he will go head to head with two other players who became peripheral under O'Neill, Nigel Reo-Coker and Steve Sidwell.
Villa, who have taken one point from three matches since launching the Houllier era with a derby success at Wolves, are also missing the injured Habib Beye and Gabriel Agbonlahor. However, Stephen Warnock, Luke Young and John Carew return, leaving Gardner under no illusions about the task ahead. "They're a top-class team. Just because they've got players missing we're not going to go there thinking we'll walk all over them. We're going to go out and play as if they have got a full-strength side. Whichever players come in will be good. We just have to get in their faces and make it hard for them."
In the last meeting, Birmingham dominated before succumbing to a fiercely disputed 83rd-minute penalty by Milner. "We've moved on," Gardner insists. "We were upset, but the decision got made. That's football."
McLeish has since recruited striker Nikola Zigic (who is "about nine feet tall" according to Gardner) and midfielder Alexander Hleb, both now showing signs of settling. Come the high noon kick-off, would the Serb and the Belarusian understand the importance of this parochial spat? "They'll know about it by 11 o'clock. They need to give everything but they're honest lads. They'll take a cut for the team and sweat for the team."
Asked whether a 100mph derby might prove a culture shock for Hleb after playing with the purists of Barcelona, Gardner laughs in mock indignation. "Why? Barcelona like to pass the ball and Blues want to pass it now," he says, fan to the fore and tongue tickling cheek. "I think we're as good as Barcelona to be honest."
How the west Midlands rivals match up
Major trophies: 22 (including one European Cup, seven League titles and seven FA Cups)
Last trophy: Intertoto Cup, 2001
Last derby victory: 25 April, 2010 (1-0, Villa Park)
Have won the last six derby games and 52 of the 118 Second City match-ups overall. They have finished sixth in the Premier League in each of the past three seasons.
Major trophies: 1 (one League Cup)
Last trophy: Auto Windscreens Shield, 1995
Last derby victory: 20 March 2005 (2-0, St. Andrews')
Last finished above Villa in 2003 and have not beaten them since 2005. Have been relegated from the Premier League twice in the last five seasons, although last season's 9th was their best in 51 years.