In Chapter 5, Claudia and Jamie go to the library to look for books on Michelangelo. Claudia assigns Jamie the task of looking for photographs of Angel, while she herself focuses on reading and remembering as much as she can.
After they return to the Museum, Jamie hides in the men's room to escape detection at closing time. He overhears workers saying that they would be moving the statue of Angel that night.
Jamie and Claudia bathe in the fountain at night in the deserted Museum. They discover "income" on the floor of the fountain - coins that people have tossed in while making wishes during the day.
In Chapter 6, Claudia and Jamie study the velvet which had been placed under the statue. They discover the imprint of an "M" in the soft material, which they believe might be proof that Michelangelo was its creator.
The children go to the Museum bookstore to find out what the "M" means. They find a book that shows that the symbol they found on the velvet is indeed Michelangelo's stonemason's mark.
On a typewriter displayed in front of a store on Fifth Avenue, Claudia types a letter to the Museum telling about their discovery. The children plan to mail it the next day, Monday.