FOR Sherlock Holmes, it usually meant an impatient client waiting below in the street. For Nero Wolfe, it was the doorbell that rang, disturbing the great man in his orchid rooms. For Poe or Walter de la Mare, that knocking on a moonlit door could signify a ghostly visitor - no one outside - or, even more mysterious, no one in the house....Well, clients I have none, and ghostly visitants don't have to knock; but as I spend most of the day at home, writing, I have learned to live with the occasional knock at the front door. I find doorbells even more startling than ghosts, and ornate brass knockers have a tendency to disappear when the price of brassware goes up; so my callers have to use their knuckles or fists on the solid mahogany door. It's a small price to pay for disturbing me. I hear the knocking quite distinctly, as the small front room adjoins my even smaller study-cum-bedroom. But sometimes I keep up a pretense of not hearing anything straightaway. Mahogany is good for the knuckles! Eventually I place a pencil between my teeth and, holding a sheet of blank foolscap in one hand, move slowly and thoughtfully toward the front door, so that, when I open it, my caller can see that I have been disturbed in the throes of composition. Not that I have ever succeeded in making anyone feel guilty about it; they stay as long as they like. And after they have gone, I can get back to listening to my tapes of old Hollywood operettas. Impervious to both literature and music, my first caller is usually a boy from the village, wanting to sell me his cucumbers or "France beans." For some reason he won't call them French beans. He is not impressed by the accouterment of my trade. He thrusts a cucumber into my arms and empties the beans on a coffee-table book that has been sent to me for review. (There is no coffee table, but the book makes a good one.) He is confident that I cannot resist his France beans, even though this sub-Himalayan v ariety is extremely hard and stringy. (Actually, I am a sucker for cucumbers, but I take the beans so I can get the cucumber cheap. In this fashion, authors survive.) The deal done, and the door closed, I decide it's time to do some work. I start this little essay. If it's nice and gets published, I will be able to pay the light bill. There's a knock at the door. Some knocks I recognize, but this is a new one. Perhaps it's someone asking for a donation. Cucumber in hand, I stride to the door and open it abruptly only to be confronted by a polite, smart-looking chauffeur who presents me with a large bouquet of flowering gladioluses. "With the compliments of Mr. B. P. Singh," he announces, before departing smartly with a click of the heels. I start looking for a receptacle for the flowers, as Grandmother's flower vase was really designed for violets and forget-me-nots. B. P. Singh is a kind man who had the original idea of turning his property outside Mussoorie into a gladiolus farm. A bare hillside is now a mass of gladioluses from May to September. He sells them to flower shops in Delhi, but his heart bleeds at harvesting time. Gladioluses arranged in an ice bucket, I return to my desk and am wondering what I should be writing next, when there is a loud banging on the door. No friendly knock this time. Urgent, peremptory, summoning! Could it be the police? And what have I done? Every good citizen has at least one guilty secret, just waiting to be discovered! I move warily to the door and open it an inch or two. It is a policeman! Hastily I drop the cucumber and politely ask him if I can be of help. Try to look casual, I tell myself. He has a small packet in his hands. No, it's not a warrant. It turns out to be a slim volume of verse, sent over by a visiting police official who has authored it. I thank his emissary profusely, and after he has gone, I place the volume reverently on my bookshelf, beside the works of other poetry-loving policemen. These men of steel, who inspire so much awe and trepidation in the rest of us, are hum an and some of them are poets. Now it's afternoon, and the knock I hear is a familiar one, and welcome, for it heralds the postman. What would writers do without postmen? They have more power than literary agents. I don't have an agent (I'll be honest and say an agent won't have me), but I do have a postman, and he turns up every day except when there's a landslide. Yes, it's Prakash the postman who makes my day, showering me with letters, books, acceptances, rejections, and even the occasional check. These postmen are fine fellows; they do their utmost to bring the good news from Ghent to Aix. And what has Prakash brought me today? A reminder: I haven't paid my subscription to the Author's Guild. I'd better send it off, or I shall be a derecognized author. A letter from a reader: Would I like to go through her 300-page dissertation on the "Bhagavad-Gita"? Someday, my love... . A check, a check! From Sunflower Books, for the sale of six copies of one of my books during the previous year. Never mind. Six wise persons put their money down for my book. No fresh acceptances, but no rejections eithe r. A postcard from Goa, where one of my publishers is taking a holiday. So the post is something of an anticlimax. But I mustn't complain. Not every knock on the door brings gladioluses fresh from the fields. Tomorrow's another day, and the postman comes six days a week.