If you happen to be taking a walk in London this week, you just might happen upon a hidden book—one that contains a note from Catherine, Duchess of Cambridge.

The royal, along with the British group the Book Fairies, hid 150 copies of her new book, Hold Still: A Portrait of Our Nation in 2020, around London late last week, People magazine reports. The book, published by the U.K.’s National Portrait Gallery, features 100 photographs of Britons during the Covid-19 pandemic.

“Each copy is adorned with a gold book fairy sticker, gold ribbon, and has a letter from The Duchess tucked inside,” reads a post on the Instagram account for the Duke and Duchess of Cambridge. “To make this activity even more special, book fairies, the Hold Still judges and participants of the final 100 images are leaving copies at places that gave them hope during the lockdown.”

Accompanying the post is a video of Catherine placing a book by a fountain near Kensington Palace, where Catherine and her husband, Prince William, live.

The note included with the book reads in part, “The Hold Still book documents a photography project which captured a portrait of our nation as we lived through the first COVID-19 lockdown last year. The images tell the stories of the challenges we all faced, but also how we came together in the most extraordinary of times.”

Michael Schaub is a Texas-based journalist and regular contributor to NPR.