When Sarah Jane Smith broke into the complex and took Eldrad's hand into the reactor room, Watson assumed that she was a terrorist intent on sabotage. However, he learned the truth from the Fourth Doctor, who also told him Eldrad's origins. This prompted Watson go order a nuclear strike on the complex to destroy Eldrad, but it was neutralised by Eldrad.
Behind the scenes Edit
While the serial only identifies him as "Watson", the novelisation gives his first name as Owen.