Tryst was a xenozoologist who went on an expedition to collect and catalogue flora and fauna from many planets in the galaxy. He used a Continuous Event Transmuter to gather samples and was accompanied by his assistants Della and Stott. The government sponsored him, but when this stopped with the galactic recession, he took to smuggling vraxoin after he discovered Mandrels were a source of the drug.
After the Empress crashed into the Hecate, Tryst tried to frame the Fourth Doctor as the smuggler, but was eventually exposed and arrested. He tried to plead with the Doctor, but was shunned as he was taken away. (TV: Nightmare of Eden)