Marcel and the Shakespeare Letters (Penguin Readers, Level 1) by Stephen Rabley

There are fireworks in London on 5th November when Marcel goes to stay with his friend, Henry. Henry lives next door to a professor who is looking after some very special letters written by William Shakespeare. When Marcel and Henry go to look at them, they are not there. Someone has stolen them! But Marcel is a detective, and he has to find the Shakespeare letters. A thrilling mystery novel featuring Marcel, the French mouse detective.