Dr Mark Lucas

In the novel Destination Unknown,  Dr Mark Lucas is an acquaintance of the nuclear scientist Thomas Betterton. Shortly before Betterton disappeared, he and his wife Olive had met Lucas at the Dorset Hotel in London. Lucas was among the contacts that British security official Mr Jessop wanted to know about while investigating Betterton's disappearance.

According to Olive, Lucas was an American research chemist, a German refugee who had taken American nationality. He and Betterton had last met in America. Betterton seemed fairly pleased to meet Lucas but later told Olive that he didn't care for him very much as he did not know him very well. It was just a casual meeting and there was no arrangement to meet again.