It was a bitter January day and when I reached college I headed for the library. The room was cold after the Christmas break. I pulled out my books with a sigh.

A woman student walked in and sat down opposite me. She was a few years older than me and had piles of soft brown hair scooped up into a bun and a pale pretty face. She wasn’t dressed like a student. She looked ladylike in a cream cashmere jumper, grey skirt and beautiful tan boots. She took her books from her bag, expensive books on history of art, and stacked these into a tower in front of her. The skin on her hands was covered with angry red marks. She did not make eye contact with me and as she started to read she kept scratching at her hands in a compulsive way. It was disturbing. I wanted to get up and move somewhere else but was worried she would know I was trying to get away from her. So I sat on, unable to take anything in from the book I was reading, listening to her scratching her hands raw.

A week later I saw her again. There's a square of grass in front of my college and a flight of stone steps leading up to the portico. She was standing by the steps. She looked smart in a cream and green tweed coat with a fur collar. But what attracted my gaze was that she was standing a bit too close to a tall older man who was looking down at her, their eyes locked. She brought up her hand and pressed her forefinger in the middle of his chest as if she was pushing him away. They both smiled at this playful gesture which spoke of intimacy, then turned and walked away from each other.

In March I was due to attend a series of seminars on Giants of the Renaissance. I walked into the seminar room and who should be sitting at the table but the pretty pale woman. And the older man I had seen her talking to was also there. The professor who was leading the seminar asked us to introduce ourselves. She spoke softly as she told us she was Isobel Lawrence and was writing a thesis on Leonardo da Vinci. He was a tutor in the History of Art faculty. They did not sit near each other and it was all formality between them this time.

Over the next six weeks the Renaissance seminars proved interesting, more because of the group dynamics rather than any insight into the art. I made a point of sitting next to Isobel Lawrence. She always dressed beautifully. But her hands were still covered with the angry red scratches and she kept her hands under the table. I became convinced that she was having an affair with the pompous tutor, Benedict Wainwright. It was not to do with anything she said; she was silent throughout the seminars. It was the way she mirrored his movements. He was always holding forth on some theory or another. If he put his head to one side she did the same. When he nodded to emphasise a point, she nodded too. She was in the grip of a deep enchantment and when I looked at him I marvelled at how that could be.

At the end of March I found out from a friend in the History of Art faculty that Benedict Wainwright was married. Was my theory about their affair correct? I decided to follow Isobel at the end of the next seminar. She and Benedict left the room separately as they always did. He headed up the main street that bordered our college and turned right. Ten minutes later I saw Isobel walking in the same direction. I followed her at a distance. She turned right too and then into a side road. She entered a small discreet hotel set back from the road. I was jubilant. They must be lovers. And I was sure now that the angry red scratches were the marks of her guilt.

The following week was the last Renaissance seminar. We trooped into the room and took our places at the table. We were to discuss a paper on Botticelli. I felt the change in the atmosphere at once. Isobel Lawrence had her head bowed and she was not looking at Benedict at all. As we sat and discussed the masterpieces of Botticelli I could sense her moving her hands under the table as if she was doing something. It was unnerving. And then she withdrew her hands from beneath the table and stretched her arms out in front of her.

She was wearing a pair of black satin elbow-length evening gloves. The effect on Benedict was electrifying. I could see guilt and anger reddening his face. And then in that stilted academic environment she did the most extraordinary thing. She started to pull the gloves off finger by finger, like a stripper, and she was looking at Benedict the whole time as if the show was for him only; as if she was oblivious to the rest of us. All discussion stopped. We were staring at her now; mesmerised by her actions. When she had taken both gloves off she bundled them and threw them at his face. He staggered to his feet; grabbed hold of the gloves as if they were red hot and dangerous and slammed out of the seminar room.

Isobel remained silent and seated at the table. It was impossible to continue our discussion. A long tense silence followed and then she spoke.

‘He finds my hands ugly. He can't bear to look at them while we’re naked. He said he had a gift for me. And he gave me the gloves.’

These were the first words Isobel had spoken at the seminars. And all I could think was that I had been right all along.

Jane Lythell is author of The Lie of You (ebook version is called I Will Have What is Mine), a chilling psychological thriller about obsession, jealousy, and female identity.