It is reckoned to be the biggest tax scandal in German post-war history.
An international group of bankers, lawyers and stockbrokers - reportedly with links to the City of London - appears to have fiddled the tax system, employing practices which were at best unethical, at worst illegal.
Ultimately they may have deprived the state of nearly €32bn (£28bn; $36bn). As the German broadcaster ARD wryly noted, that would have paid for repairs to a lot of schools and bridges.
The newspaper Die Zeit adds that the sum would more than cover the cost of the refugee influx for a year.
Prosecutors have been investigating for some time. And gradually it is emerging that large-scale tax avoidance was taking place right under the noses of the authorities.
And that - in some cases - they turned a blind eye to practices employed, not just by individuals out to make a fortune, but by some of the country's biggest banks and respected businesses.
We may never really know the full extent of those practices; largely because they involved fiendishly complex transactions, which German media broadly divide into two kinds.
In the first type, German banks and stockbrokers bought and sold shares for foreign investors in a way which allowed them to claim a tax refund for which they were not eligible. Many question the legality of the practice.
In the second (a more complicated variation), investors and banks bought and sold shares just before and just after dividends were paid. With a bit of imaginative paperwork, and by exploiting a procedure which allows more than one person or institution to simultaneously own a share, they were able to claim numerous tax refunds. The practice was outlawed in 2012.
German prosecutors are investigating a number of banks - among them institutions which were bailed out by the state - and individuals.
But in the meantime, a group of German journalists has been researching too, working alongside an expert from the University of Mannheim.
Their investigations, broadcast on Thursday night, reveal that, despite a warning from State Commissioner August Schäfer in 1992 and the testimony of five whistleblowers, the practices continued and were widespread.
They involved 40 German banks and scores of other financial institutions around the world.
And, as those German reporters reveal, in the end it wasn't a national authority, a finance minister or the justice system who finally exposed the practice.
It was a young administrative assistant in Germany's central tax office, who noticed that she was receiving claims for huge tax rebates from a single US pension fund.
Anna Schablonski (a pseudonym) dug further and, despite threats, began to uncover other cases. She is modest about her role - even though 30 colleagues are now dedicated to trying to recover some of the money, and prosecutors are building their cases against some of those involved.
She does not want to be cast as a hero, she says. She was just doing her job.