This is aimed at readers aged 8-12 and it is a brilliant adventure where you can't resist keep turning the pages. But it's got a quite sophisticated feel about it. The line drawings which illustrate the book throughout are realistic - rather than comic or childish. And the (plausible) dastardly plot at the centre of the book could easily trouble an older reader! 

Isaac Turner loves watching his dad at work and this day was particularly special because they're both in the belfry of Big Ben overseeing the clock going back for daylight saving time.

While Isaac struggles to understand the purpose of changing the clocks twice a year, his dad tells him that Parliament is currently considering an even more radical idea - to make time metric.

Continuing with the task in hand, Diggory Turner leaves Isaac momentarily, but then doesn't return. There's nowhere he could have gone but all that's left of him is a smashed pocket watch and a mysterious message. It's left to Isaac to find out what's happened. 

Isaac is at first taken in by his godfather, Solomon, the speaker of the House of Commons and is introduced to Hattie, Solomon's daughter. Together the two children probe the Houses of Parliament and London landmarks for answers to Diggory's disappearance.

It's a locked-room mystery packed with rooftop chases, hidden codes and 'mind-bending science'. Pursued by malevolent actors, they don't know who they can trust, but they need to find answers because there are implications for national and international security. 

This is a brilliant story which is clever and thought-provoking. There are also a few fascinating facts woven into the plot, revealed at the end of the book. It's written by one of the team who created the Adventures on Trains series, which are also fantastic!