Repeat as necessary to bulk the story out to 4 episodes. But hey, the classic series totally made full and excellent use of its stories' running time, didn't it? Some fans advocate destroying the sonic screwdriver, as they see it as preventing the writers from including 100 captures and escapes in every story; on the other hand they did that back in Fivey's run and it made no difference, not even in the story they destroyed it in.