This Vatican thriller, the debut of the New York lawyer Roger Crane, was a popular success at Chichester in April. In this West End transfer, it looks a little mechanical, the cogs and wheels of its plot workings plainly visible as it advances speculative theories surrounding the untimely demise of the “smiling Pope” John Paul I.

But the great strength of David Jones’s production is its performances, chief among them David Suchet as Cardinal Benelli, right-hand man of John Paul I’s predecessor and the architect of the reluctant Albino Luciani’s ascent to the papacy he would hold for a mere 33 days before his mysterious death.

Suchet’s Benelli is a darkly silky creature rent by a mounting crisis of faith and by his guilt over his unwitting complicity in Luciani’s destruction. With Machiavellian political adroitness, he manoeuvres into power the man who possesses the true Christian virtues of humility, gentleness and simplicity – and who will introduce the liberal reforms that Pope Paul VI never got around to.

With potent containment Suchet shows us how his view of Luciani shifts; from seeing him as useful pawn, he begins to regard him with envy and even awe, his simple belief in marked contrast to Benelli’s own tormenting doubts. Richard O’Callaghan’s Luciani, meanwhile, at first a diffident, tremulous figure in oversized spectacles, turns out as Pope to be both twinkly and tough. In his new white robes, surrounded by hostile bishops and cardinals in blood-red and crow-black, he looks like a lamb to the slaughter. In Crane’s version of events it is his innocence and integrity, in the face of the reactionary Curia’s machinations, that kill him.

Also excellent among a strong ensemble are Stuart Milligan, wolfish as Bishop Marcinkus, head of the Vatican Bank and associate of the ill-fated Roberto Calvi; and Bernard Lloyd as Secretary of State Villot, ruthlessly, and with a mounting sense of suppressed panic, defending the status quo.

The play loses momentum after Luciani’s death, and the debates surrounding the tensions between church and state, spiritual and material, human and divine don’t emerge quite strongly enough. But when the powerplay between well-drawn characters is as finely acted as here, it grips.

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