A series of classic British Airways ads are book-ended by two newspaper headlines: "BA is bloody awful" from 1982, just before Saatchi & Saatchi took on the account, and "BA becomes the world's most profitable airline" from 2005. And the M&C Saatchi sign-off - "Now taking new airline bookings" - is typically confident.
But sure as hell, beneath the bravura, the agency has been dealt a massive body-blow. If there is one account that has characterised M&C Saatchi, helped define its DNA, and given the agency a stature that belies much of the rest of its client list, then BA is it.
The BA account has provided a platform for M&C's international expansion, gave its AIM flotation last year extra oomph, and has allowed the agency to punch above its weight on the international stage.
Of course, BA has got its money's worth and then some. There is no denying that the Saatchis team, when they were at Saatchi & Saatchi, played a vital role in building BA into a global phenomenon. The "world's favourite airline" was a masterstroke and some of the campaigns - "Manhattan" and "face" particularly - are among some of the best UK ads of the last century.
And, hell, a client relationship that survives for 23 years is a pretty astounding achievement in advertising these days.
But, but, but. M&C's work for the airline has been unspectacular over the past few years. BA is no longer the institutionalised, establishment-heavy corporation it was when Colin Marshall was at the helm. And BA - still smarting from the Gate Gourmet farrago - is under new cost pressures as it prepares to move into Heathrow's Terminal Five.
Everything was pointing towards the time being right for funda-mental change.
For M&C this is its first real test as a public company. With a group of demanding shareholders and critical analysts now breathing down its neck, the agency needs more than chutzpah to see it through. OK, BA apparently accounts for 7 per cent of the agency's revenues - not much, on the face of it. But in truth, BA has represented an awful lot more than that to M&C Saatchi's fortunes.
BA's presence on M&C's client list was no doubt both a comfort and a lure for existing and potential new clients. And the BA account was surely embedded in M&C's plans to open new offices in key markets around the world, offering real proof that the micro network is capable of handling international business and prestigious clients.
What's more, it's estimated that the loss of BA could wipe £2.5 million off M&C's pre-tax profits next year. So the City will now be looking for a clear, early signal of how the agency plans to fight back.
M&C has impeccable airline credentials - but the airline business ain't what it was and the number of carriers with anything like BA's status and budgets are hard to spot. Certainly the notion of replacing BA with, say, easyJet - which is currently reviewing its advertising arrangements - would be like resorting to a corn plaster when you've just had a limb torn off.
Of course, M&C Saatchi will pull itself back from the BA blow, and the agency's confident newspaper advertisement this week is a clear signal of its determination to do just that. But the chances of finding another client with the same combination of long-term loyalty and international prestige as BA are virtually nil.
As more details emerge of quite how much Interpublic's agencies are trying to hand back to clients in a bid to clear their corporate conscience, quite a few advertisers can expect a windfall.
But you have to wonder whether the clients will be pleased with the payback or disgusted that they've potentially been taken for a ride.