IT WAS Saturday afternoon and the branch library was deserted except for two other customers and the librarian at a computer behind the counter. I had been browsing for about 10 minutes when a big, elderly man shuffled down the aisle and noisily put down a carrier bag of shopping and a brown holdall.

I continued scanning the spines for a minute or two, then I noticed the slow, deliberate movement of a hand, and the name Christine, above a picture of Stephen King, disappear into the man's black trenchcoat. As he turned towards me - he was only feet away - I busily picked a book from the shelf and inspected the blurb. He lumbered past and headed across to the far side of the library.

The librarian was still busy at his computer and I wondered whether I should tell him what I'd seen. It was doubtful that this customer intended borrowing a book he had so surreptitiously concealed. I decided to wait and see. If he didn't offer the book for stamping, I'd inform the librarian before he left.

I kept the man in sight and walked over to the paperback rack. He flicked through Cooking for One before slipping it into his holdall.

I kept the man in sight as he perused science fiction paperbacks. Holding three or four in one hand, he took another from the shelf while dropping the others into the holdall.

As he made his way towards the reference shelves, I positioned myself by the Mills & Boons. He pulled out a Guinness Book of Records, opened it, and earnestly studied a page. Abruptly closing it, he put it under his left arm and reached for Roget's Thesaurus on the top shelf. This also went under the arm. A dictionary came next, and then suddenly he glanced round. I fingered the Mills & Boon spines and he headed back to the reading area and sat down.

I glanced at him and he caught my eye as he zipped up his holdall. Although he had no reason to guess I should find this suspicious, something in his eyes registered that I knew what he was up to. The unease we shared seemed to last an age.

I half smiled at him and he looked away. At the reference section, he unzipped the holdall and casually returned the Thesaurus and dictionary. Clearly then, he was prepared to take a risk, hoping that I hadn't seen him bagging any books. However, labouring across to the cookery section, he retrieved another book from the holdall and then carefully replaced it on the top shelf. Not once did he look round. He probably thought I had rumbled him earlier, if not from the start, and now had to decide whether I knew the number of books he had taken.

He was prepared to take the risk. He approached the counter. I reckoned he still had five or six books about him. From inside the holdall he took a cookery book and placed it on the counter. It was stamped and returned to the holdall, pleasantries were exchanged. But as he picked up his holdall, one of the handles came away. The bag swung and two books spilled on to the floor.

The librarian noticed them, as well as two more inside. Ashen-faced and on the verge of tears, the man looked at me for the second time. I glanced pointedly at his coat and like an embarrassed conjuror he pulled out the copy of Stephen King's Christine.

'Regretfully, I'm going to have to inform the police,' the librarian said. Defiantly, the thief tossed the Stephen King on to the counter. 'It's a mistake,' he said. 'I'd forgotten about the other books.' He wanted to leave, but the librarian demanded that he stay until the police came.

When they went to the man's house, the police found shelves lined with stolen library books worth more than pounds 500. He was let off the hook after he had paid his outstanding library fines. Funnily enough, the thief was allowed to retain his membership. I've seen him in the library a couple of times since. He doesn't acknowledge me, but he's very polite to the librarian.