While I find it easy to accept that Robert Maxwell was a villain with some redeeming features, I remain unconvinced that the saintly Mother Teresa of Calcutta existed beneath a somewhat tarnished halo. This, in a sentence, is my major problem with Ian Curteis's entertaining new play The Bargain, at Milton Keynes Theatre this week. One of two major problems, in fact. The second - which is always to be found in semi-factual dramas about real people - is that you are never sure how much of it has been made up.

The highly experienced Curteis says in a programme note that the action is closely based on fact. "The questionable business operations" Cap'n Bob was carrying out at the time of his meeting in London with Mother Teresa "are well documented", he tells us. That's as maybe. Perhaps he would care to point to the document that indicates that Mother T. was prepared to collude in a spot of big-time international money-laundering in order to further the spread of her worldwide mission. This dramatic conceit, as presented here, becomes even less likely, since we find the nun in the company of a very business-savvy Sister, excellently played by Susan Hampshire. This appealing character, as well as possessing an impressive knowledge of the Turf, develops - further straining credibility - a tendresse for Maxwell's much-bossed-about assistant (Jonathan Coy), who is known only as Side Kick.

Sister is twice referred to as "Number Two Nun", a joke missed by the whole first-night audience, who clearly knew nothing of Charlie Chan and his family. Curteis is on safer comic ground when he gets Anna Calder-Marshall's Mother Teresa to discuss an abortive fund-raising meeting with Margaret Thatcher and even to give an impersonation (!!) of the Iron Lady.

Icon of the age as she was (even Princess Diana was obliged to share the front pages after their oddly coincident deaths), most people, I suspect, have no idea what Mother Teresa sounded like (though we can be fairly sure it was not like Mrs Thatcher). In giving her a thickish East European accent, Ms Calder-Marshall presumably 'gets it right' for the Albanian-born nun, even if she doesn't look much like her.

Michael Pennington, on the other hand, has the task of presenting a character whose voice is almost as familiar as his face. As it happens, his tones - by turns wily, authoritative, persuasive and angry - were the first thing I heard on the radio (tapes of his telephone calls) on the morning that I wrote this review. This confirmed, as I had already suspected, that Mr Pennington was spot-on in his vocal impersonation, as well as looking uncannily like the fat fraud.

His performance (and Mr Curteis's writing) perfectly catches the way that Maxwell's demeanour could change on an instant from beaming bonhomie to ranting fury. Such is the way, of course, that tyrants inspire the fear that is the key to their control over others. Especially touching were the scenes in which Maxwell described the hardships of his Czechoslovakian upbringing and the suffering his family endured at the hands of a much worse tyrant than he, Hitler.

A welcome humour shines through occasionally, too. I loved the moment when he explained that it was his sunny, up-tempo demeanour - and not his financial irregularities - that led others to call him "the Bouncing Czech". A lie of this sort shows real chutzpah.