THE TIME THIEF, by Patience Agbabi
"It's mid-summer's day and thirteen-year-old Elle and her Leapling classmates are visiting the Museum of the Past, the Present and the Future. But on the day of the school trip, disaster strikes, and the most unique and valuable piece in the museum, the Infinity-Glass, is stolen! And worse still, Elle's friend and fellow Infinite, MC² is arrested for the crime! To prove his innocence Elle must leap back centuries in time, to a London very different...