One of the most famous things written about any financial institution is the line of the American writer Matt Taibbi about Goldman Sachs: "A great vampire squid wrapped around the face of humanity, relentlessly jamming its blood funnel into anything that smells like money." It seems that the Securities and Exchange Commission, the body that polices the US financial industry, agrees. Friday's news that the SEC has launched a civil action against Goldman Sachs was astonishing to the world of money, not so much because the underlying events were astonishing, but because of the SEC's manifest determination to come after the world's richest and most powerful investment bank.

The sort of activity Goldman is alleged to have committed has already been the subject of a roasting for the bank's boss, Lloyd Blankfein, at the US Congress hearings on the credit crunch. The nub of the charge was that Goldman was helping some clients to make huge bets against the very same mortgage-backed assets that it was energetically selling to other clients. As the inquiry chairman put it, the bank was "selling a used car with faulty brakes and then buying an insurance policy on those cars".

Blankfein didn't even pretend to hide his irritation, and replied: "That's what a market is." The buyers knew what they were doing, and the sellers were free to take a different view. Is it really a market, though, if one side knows what is happening and the other doesn't? That is the argument – not far off being a philosophical debate – on which the case will turn. Goldman's line of defence is already clear from its PR material. The first three sentences of its press release twice mention the fact that the fraud case concerns a transaction between "two professional institutional investors". In other words, Goldman is planning the 10CC defence: "big boys don't cry".

The very best book about this whole affair is Michael Lewis's new book The Big Short. Lewis worked at Salomon Brothers in the early 80s and wrote a brilliant book about it, Liar's Poker. Lewis now admits that he thought he was writing a furious anti-money diatribe, but his book was instead treated as a manual about how to get ahead in the amoral financial world of the 80s and after. Now he's gone back to Wall Street to write a kind of follow-up, about how the excesses he had described went unchecked for more than two decades, and ended in disaster. The heroes of the story are the people who diagnosed the credit bubble early, and bet hugely against it.

The Big Short is, among other things, a blistering, detailed indictment of the way Wall Street does business, and its particular villains are the investment banks. One thing that emerges clearly is how much the banks love opaque new financial products. Collateralised debt obligations of the type involved in the Goldman case were fancy new inventions with no clear rules, no free market, and no transparency – all features that were, from the banks' point of view, great news. They could make them anyway they wanted, sell them any way they wanted, price them any way they wanted. It was beautiful. It's impossible to read Lewis's book without concluding that, in the course of the CDO fiesta, lines between right and wrong were repeatedly crossed. The SEC lawsuit will turn on the much narrower issue of whether lines between legal and illegal were also crossed.

My hunch would be that Goldman is much less worried about this specific case than about what else the investigators might find, once they get into the bank's affairs and start sniffing around. As Lewis puts it: "Goldman Sachs is, to put it mildly, unhelpful when asked to explain exactly what it did, and this lack of transparency extends to its shareholders." A big bank can usually ignore its shareholders, but the authorities are unlikely to just ask nicely and then leave it at that. In the US it is a crime to lie to a federal agent, and it's often this that sends people to jail over financial matters. (Martha Stewart would have got away with insider trading; it was lying to the Feds that landed her in the clink.) No bank wants the Feds sniffing around, asking its employees awkward questions – and although this case is for the moment only a civil suit, that could change pretty fast.

So the question is: will the Feds find anything? I'm not going to hold my breath. One of Lewis's subjects notices that when his trader at Goldman has anything awkward to say, she says it over her cellphone, because landline calls from the bank are taped. "If a team of forensic accountants went over Goldman's books," one insider observes, "they'd be shocked at just how good Goldman is at hiding things." If there were to be any evidence of illegal activity at Goldman, it would be buried very, very deep.

In The Hitchhiker's Guide to the Galaxy, a notice ordering the demolition of someone's house is found "on display" in a lightless, stairless cellar, in the bottom of a locked filing cabinet, in a disused lavatory, with a sign on the door saying "Beware of the leopard". The SEC will be lucky if it's as obvious as that.