It began with a chance encounter at a New Year's party in 2004. I was trying to leave, but a woman said she had a message for me. She knew I had been a journalist and she had a friend who wanted my help to solve a family mystery. I agreed to a meeting, and found myself embarking on a five-year quest for a man I had never met.

The woman's friend was called Jane, a financial administrator from St Albans. She was in her late 30s and had been through an emotional experience. Just before Christmas, her mother, Philomena, tipsy on festive sherry, had revealed a secret she had kept for 50 years – she had a son she had never mentioned to anyone.

Jane said her lost brother would be in his early 50s and probably living in America. The reason for the secrecy was that he had been born outside of marriage in Ireland at a time when such things were considered shameful.