Rex can't wait for his first trip to the city museum. But, hold on, are those ... bones? Dinosaur bones?! It turns out that museums can be scary places. And now, someone or something has been causing havoc around the place and it's up to Rex, Sandra and the gang to find out who. Can Rex successfully go undercover as the new security guard? How can he help his newest unexpected friend, an Ancient Egyptian mummy? And most importantly, can he pull off the greatest museum sleepover in the history of sleepovers? Highly illustrated throughout and laugh-out loud hilarious, this is perfect for fans of The Bolds, Dogman and Bunny vs Monkey.