Diana Wynne Jones

time patrol n.	1987 D. W. Jones Tale of Time City (1989) vii. 99 ‘What happens,’ Vivian asked, ‘if a tourist meets his own grandchildren and hates them and decides not to get married? Wouldn’t that change history?’ ‘There’s a whole branch of Time Patrol checking to make sure that won’t happen,’ said Ramona. ‘Hush, Sam.’