In 2016 the great London agent Ed Victor, and the equally formidable Graham C. Greene, a nephew of the novelist, asked me if I would consider writing a sequel to the Philip Marlowe novels that have periodically appeared since Raymond Chandler’s death in 1959. The offer, as you might expect, was gentlemanly. Robert B. Parker and the novelist John Banville would be my only predecessors, having between them published three Marlowe novels between 1988 and the present. The sequels began with Parker’s “Poodle Springs,” a completion of Chandler’s last novel, then continued with the same author’s “Perchance to Dream,” in 1991, and culminated with Banville’s “The Black Eyed Blonde,” published under his pen name Benjamin Black in 2014. I was told that I could do more or less whatever I wanted — within reason. But what was within reason?

My first impulse was to turn the offer down. I revere Banville as a stylist, not to mention Chandler himself, and it seemed hazardous to try to compete with both of them at the same time. I surely couldn’t win that one. Apart from anything else, fans of both would probably be propelled into a tediously predictable state of ire. So what was the upside? There was vanity, of course; and then there was curiosity, the demon that killed the cat. So far, so treacherous. But there were also possibilities. I wrote back to the Chandler estate to ask whether its executors might consider my making Marlowe old, alone and desolately marooned in the year 1988. Would it fly with them, or indeed with Chandler’s fans? Would they mind seeing him in the age of Ronald Reagan and Slash?

I thought to myself that before accepting I would write 40 pages set in Baja in 1988 and see if the resulting Marlowe-in-dotage gave off the delicious sparks that a character must generate if his creator is to stay the course. If the pages worked, I’d accept the commission and stand by the decision. Presented with the whole novel, they could then see if I had wasted my time, and theirs. It was not a small gamble.

But to begin with it was an exercise, a speculative ventriloquy. The cadences of Chandler, the inner world of his knight-errant (a thinly disguised version of the hero knight of Sir Thomas Malory’s “Le Morte d’Arthur”), the quick-stepping wisecracks and beautifully compressed metaphors — all of this could be echoed in some way. But tricks of that kind are bound to weary a reader looking, as all readers do, for authenticity of voice. Little by little, something else has to happen. In the end, you’re condemned to write your own book. A pastiche or historical period piece would never have worked for me anyway. As Salvador Dalí used to say: “Don’t bother about being modern. Unfortunately it is the one thing that, whatever you do, you cannot avoid.”