“An Evening with Nick Cave” was partly a book reading, partly a Q&A session and partly a rock concert. It was also turning into a dog’s dinner until Cave’s ex-lover, the singer P.J. Harvey, present in the audience, was persuaded to join the Australian for their 1996 duet “Henry Lee”. Cave looked startled, like one whose show was being hijacked, but the unscheduled reconciliation provoked his best performance of the evening.

The occasion celebrated the publication of Cave’s second novel, The Death of Bunny Munro, a scabrous black comedy about a sex-obsessed travelling salesman. The subject of middle-aged men behaving badly, chronicled not only by Bunny Munro but also in recent albums with his band The Bad Seeds and his side-project Grinderman, has given the 52-year-old a new lease of life. Formerly infamous for his violent music and drug-addicted lifestyle, Cave, now a settled family man living on the English south coast, has turned himself into a Martin Amis-style satirist of male depravity.

But there was not such a happy balance between fiction and music at the Palace Theatre. Three readings from the novel were set to music played by long-standing collaborator Warren Ellis. They were also joined by Bad Seeds bass-player Martyn Casey for reworked versions of Cave’s songs. The mood was improvisatory. “This isn’t as rehearsed as it looks,” Cave muttered, hunting for lyrics among the piles of paper on his piano.

Bunny Munro is a fine novel, but the readings didn’t do it justice. The soundtrack was skimpy, and the final passage, a disturbing account of a sexual assault, was wrecked by Cave losing his place. And the questions he invited from the audience chiefly consisted of banal queries about places he hadn’t visited or a B-side he’d forgotten he’d written. Fan: “It’s your best song!” Cave, puzzled: “Is it?”

Music dominated the set, with Cave, Ellis and Casey imaginatively reworking old Bad Seeds numbers. “The Mercy Seat” was turned into a forceful piano ballad; “Tupelo” had a bare-bones, psychotic energy. Yet the biblical thunder and gothic balladry sat awkwardly with Bunny Munro’s grotesquerie, with only the sleazy garage rock of “Dig, Lazarus, Dig!!!” from his latest album properly chiming with the novel.

Then came Harvey’s appearance, prompted by an audience member asking Cave if he would duet with her. He hummed and hawed (“If it was the other way round, I’d be mortified”), but a magnificent rendition of murder ballad “Henry Lee” followed, Harvey initially sounding unpractised but growing in power as the song progressed.

Something sparked in Cave, and he ended the set playing with a hitherto absent intensity. Ironically, the first song of the evening had been “West Country Girl”, written about Harvey after they split up in the mid-1990s. As if illustrating Cave’s preoccupation with middle-aged male decline, tonight his ex-girlfriend stole the show.