I didn't know just how immoral the International Monetary Fund could be until I saw Beth Steel's latest play. According to the programme notes, the famous institution was created in the wake of the Great Depression and the Second World War. Here at last was an organisation intended to promote international financial stability, facilitate trade, high employment and sustainable growth thereby reducing poverty around the world.

But there's a scene in Labyrinth that convincingly suggests how the IMF could work in the real world. The play is set in 1982, in the office of Mexico's Finance Minister. The country has just defaulted on its debts and on the other side of the minister's desk sits an IMF official and the hero-cum-antihero of Steel's play, a young American banker called John, played by the terrific Sean Delaney.

Up until this point we have followed John's rise through a Wall Street bank and have got to know him pretty well. Unlike most of his Ivy League peers John, the son of a small-time crook, clambers up the corporate ladder with a drive instilled in him by childhood poverty. He works harder and learns faster than those around him. He will never have money problems again, he declares. Except it doesn't quite work out that way.

The debts that Mexico have defaulted on were mostly the result of John's rose-tinted - for which read misleading - reports, albeit written at the behest of his young-gun mentor Charlie (Tom Weston Jones) who personifies the banking culture of 'sell debt at any cost' as long as it's the borrower's.

Anyway, back to that tense scene in the Mexican Finance Minister's office which arrives latish in Steel's play. John, whose arrogance has been frazzled into humility by the realisation that he has fatally exposed his bank, is attempting to negotiate a bail-out as the IMF lady insists that Mexico agrees to reforms and austerity.

This, protests the finance minister, will hit the poorest workers, who have an average age of 15. "You're hurting children," he rages. John counters this argument by highlighting the corruption that has lined the pockets of the finance minister and his friends. But the calm IMF rep says this group could be protected because they, after all, are the failing country's "modernisers".

This, for my money, is the dynamite in Steel's play. The scene is a superbly illustrated indictment of an international institution whose no doubt well-paid executives are seen secretly increasing poverty while protecting those who caused it.

But this point is so buried in a hoary old narrative about amoral international corporations, that Steel's bombshell has the potency of a damp squib.

For all the slickness of Anna Ledwich's production, almost every political point and observation made here - other than the outing of the IMF - has in dramatic terms, long since gone stale. They are slices of warmed-up toast offered as pearls of wisdom.

Lucy Prebble's Enron, Caryl Churchill's Serious Money, David Hare's The Power of Yes - to name but three well-known plays - have all targeted the greed of corporations and financial institutions such as the City of London. A play needs startling originality if it is to target bankers who, along with journalists and politicians (also represented here) are the world's most vilified professionals. This one has apparently been written with the cliché radar turned off.

"Owe a bank a hundred dollars and it's your problem. Owe it a hundred million, it's the bank's problem," is one dusted-off piece of dialogue. Even the attempt to flesh out John's emotional life - a plot about his feckless father with a twist which is predictable well in advance of its arrival - has the feel of off-the-shelf narrative.

The saving grace is Delaney. This is his second show after making a memorable debut as a supporting character in David Lindsay-Abaire's play Rabbit Hole, which was also at the Hampstead.

This time he has rightly been given the lead and if I were to predict a star in the making - career death for most actors - it would be him.

He has that fascinating combination of innocence and latent threat which in Hollywood is the stuff of Matt Damon. Here, he carries and saves the day.