The Time Travellers and the Royal Plot

Chip and Skip haven't had a time-travelling adventure for a while, but it's Chip's birthday and neither can think of a better way to spend it. Once again, the magic glasses catapult them into the past, this time to 1953 and Queen Elizabeth's Coronation.
But when they discover a plot that could ruin everything, the time travellers have to think fast, outwit the criminals and stop history being changed forever. Can they do it - and get back in time for Chip's party?