A man made god meets God made man in John Wolfson's apocryphal drama. Leaping off from a fragment of text excluded from the biblical canon, The Inn at Lydda brings together the dying Emperor Tiberius and the resurrected Christ; a face-to-face that pits hubris against humility, and serves a corrective to earthly power.

Like most Roman Emperors, Tiberius was a tyrant. The original text stops with his seeking Jesus, hoping to be healed as death encroaches, only to learn of the crucifixion en route to Jerusalem. It lays out the death of Pilate; executed for executing the one man that could have cured Caesar. In extending that to an actual coming together, Wolfson neatly exemplifies the core of Christian faith. To be healed, and by extension forgiven, Caesar must believe the man he meets really is the risen Christ. Jesus, in turn, must absolve and heal him, in spite of all his murderous actions, if he truly repents. That's the nub of Christianity: "Whatever things you ask in prayer, believing, you will receive." Matthew 21:22. Through faith is all forgiven.

The resonance is not just religious, however, but grows out of a dialogue between opposing understandings of power. Where Tiberius exemplifies elevated sovereignty, the emperor as all-powerful protector, Christ is the opposite. He embodies leadership as a lowly act, not separate from, but as part of, the people. With the emperor-in-waiting, Tiberius' deranged nephew Caligula, also present at Lydda, Wolfson lays out the slippery slope of such earthly gods.

Played with comic brio by Philip Cumbus, impetuous and imbecilic, the partyboy prince need only click his fingers to get his way, ordering up orgies and dispensing with morality entirely. Little wonder Matthew Romain's soft-spoken John, as mad with grief as Caligula is with power, rails about the end of the world ahead of writing Revelations. The future, as Caligula, gleefully notes, will belong to the autocrats. We might see these ancients as uncivilised brutes, but our own contemporary rulers will sow more bloodshed than the emperors ever managed.

That's a mark of the writing's self-awareness, but a play that starts with the three Magi bemoaning the lack of a decent calendar becomes jaunty on account of Pythonesque humour. It's not so much that the comic subplot about a runaway prostitute (Jessica Lilley) and the emperor's doctor (David Cardy) intrudes on the serious endeavour, but that its bathos bleeds into the body of the play. Stephen Boxer's Tiberius, tickled with insanity, arrives cradling a beaver he's brought back to life, and always seems too slight and silly to truly contend with Samuel Collings' serene, commanding Christ. The dice are always stacked in Jesus's favour, greatly diminishing the drama of their intellectual duel.

Nonetheless, it's briskly handled in Andy Jordan's congenial production, taking the play as it comes, wonks, warts and all. Nick Powell's plucky cello underscore deftly lightens and darkens the mood, though it's a cop-out to introduce electric lights into the candlelit Sam Wanamaker space. It flattens a space that can be so unworldly, just as Wolfson's comic swerves drag down its spiritual contemplations.

The Inn at Lydda runs at the Sam Wanamaker Playhouse until 17 September.