Lauren Hudson was a telephone operator on Earth in 1974. She was infected by a virus engineered by the Viyrans. This caused her to dial and receive telephone calls to and from wrong numbers, which always resulted in an extremely fortunate outcome for herself or the other party. Many of her wrong numbers were to and from the Sixth Doctor, whom she began helping in his investigation of the virus by keeping track of her wrong numbers.
During one of their telephone conversations Lauren expressed her desire to get away from her boring job, and the Doctor quoted her a proverb about hard work and luck by Thomas Jefferson. Lauren's next wrong number was to a radio DJ who just happened to be asking the source of that quote for a trivia quiz. As a result Lauren won the biggest prize ever given away on British radio: a holiday for two in Marbella and spending money. She decided to bring her friend Connie Pickerill on the holiday with her. While celebrating with Connie, Lauren received another wrong number from the Doctor, who was in jail and needed someone to arrange a solicitor: a favour Lauren was able to grant him, thanks to the prize money.
Some time later, after trying and failing to re-establish contact with the Doctor via wrong numbers, Lauren decided to write him a letter instead. Not knowing where to send it, she decided to just write "the Doctor" on the envelope and hope it found its way to him. In the letter she expressed her hope that the Doctor was able to solve the mystery of the virus, and asked him to get back in touch. (AUDIO: Urgent Calls)