I followed her bus to the nearest town and when she got off I parked and saw her hurrying towards the train station. Inside, I saw her queuing at the ticket office and I managed to stay hidden behind a magazine stand while I listened to her ask for a ticket to a town in Suffolk, twelve miles away. I knew I’d never be able to get on the train without her seeing me, and I wouldn’t be able to get there before her in my car, so for that day, frustrated and more confused than ever, I gave up and went home.

The following week, however, I was ready for her. As soon as she came down for breakfast I made an excuse about wanting to get to work early and drove straight to Suffolk. I arrived in a large market town not very far away from the village Doug and I grew up in. When I got there I parked and, sure enough, ten minutes later saw her emerging from the station. Keeping a safe distance behind, I followed her as she headed into the town’s centre. Eventually, to my astonishment she came to a large building with a sign outside that said, ‘Crofton Hill Sixth Form College’. As I loitered at the gate I saw her approach a bench near the main entrance, then sit down to wait.

At eleven o’clock students began to pour out of the college doors and a tall, pretty, dark-haired girl a year or so older than Hannah walked towards my daughter with a wide smile on her face. When she reached her, Hannah got up and the two girls hugged. I was dumbstruck. Who on earth was she? Was Hannah secretly studying here? I was utterly confused. I watched as the two linked arms – such an easy, affectionate gesture, and so unlike anything I’d seen my daughter do before that my astonishment deepened. When they turned in my direction I hurriedly ducked out of sight, concealing myself behind a parked van. A few minutes later I saw them heading back into town so I followed them to a café where they sat down together at one of the outside tables.

I watched them for about an hour. Hannah looked so carefree and happy, so entirely different from her usual self as she smiled and laughed that I felt a wave of sadness, even jealousy for this stranger, whoever she was. When, finally, the girl looked at her watch and grimaced, they both got up and hugged again, before going their separate ways, leaving me to drive home alone, still entirely confused.

For three weeks I remained none the wiser, and then, one morning everything suddenly became horribly clear.