Of all the dark the dark days that Tesco has seen recently, September 22nd was the blackest.
That was when Britain's biggest grocer--and the world's third-largest retailer--confessed that it had overstated its already dismal profits for the first half of its fiscal year.
They were 850m ($1.4 billion), not 1.1 billion, as Tesco has said in August.
Its share price has slumped by about 15% since the disclosure. Credit-rating agencies hace put its dept on watch for a possible downgrade.
Tesco's accounting fiasco (see article) follows a series of profit warnings and the ousting in July of its boss, Philip Clarke.
His successor, Dave Lewis, has promised "a comprehensive independent investigation" and suspended four executives, including the chief of the company's British business, its biggest unit.
Serious questions are being asked about how such a huge, established company could get into such a mess.
Do its directors know too little about selling groceries?
None of the ten board members has direct experience of managing a retailer.
Is Mr Clarke somehow to blame?
He was said to be a micro-manager, and several executives have left, including the chief finance officer in April.
Did Tesco have a corner-cutting culture? Analysts have worried before that its accounting policies were more adventurous than those of its peers.
Whatever investigators now find in Tesco's books, it is clear that its problems go deeper.
They started under Mr. Clarke's much-praised predecesssor, Sir Terry Leahy, who widened Tesco's lead over its rivals but built too many big stores and led ill-judged forays into foreign markets like America.
Its profitability, as measured by return on captical employed, fell by one-third between 1998 and 2010.
When Mr. Clarke arrived, he splashed out on store upgrades but let Tesco's prices creep up, driving away customers.