If You're Reading This, It's Too Late is the second book in the Secret Series. It is based on the sense of hearing, and the "artifact" in it is the Sound Prism.

If You're Reading This, It's Too Late is the sequel to The Name of this Book is Secret in the Secret Series by Pseudonymous Bosch. It was released in October 2008 and features the same characters as the first book. The sequel to this book, and the third book in the Secret Series, This Book Is Not Good for You, came out on September 1, 2009 to Amazon customers and August 31, 2009 to consumers that visited Barnes and Noble that day. The Barnes and Noble version came with an exclusive card telling you a number to call to find clues to the identity of Pseudonymous Bosch.

First, Cass and Max-Ernest are back in school, where it is revealed that there is a new student from Japan: Yoji. The three of them start talking to one another, much to the annoyance of Amber. Later, their new geography teacher takes them on a school trip. This happens to coincide with a secret message Cass found in her lunch pack, as they were apparently asked by Pietro to arrive at a harbour near the site of the school trip.

After locating the rezendevous point, Cass and Max-Ernest were elated to see a sleek schooner apporaching, believing that the Terces Society was about to formally welcome them into the fold. At first, Cass is uneasy at how Pietro resembled Dr. L, but then brushes her misgivings aside due to the fact that Dr. L and Pietro were twins. Unfortunately, Max-Ernest and Cass were captured and bound almost immediately, and Cass laments her foolishness for believing Dr. L to be Pietro so eagerly.

Dr. L and Ms. Maivais then explain that for 500 years, the secret society of the Midnight Sun has been waiting for the homunculus, the man-made man, to rise, and now the evil Dr. L and Ms. Mauvais are going to throw Cass and Max-Ernest to the sharks unless they tell them where he resides. The reason why Ms. Mauvais vehemently insists that they know the whereabouts of the homunculus and the alchemist’s grave is due to the fact that Cass’ sock monster greatly resembles the homunculus.

As Max-Ernest and Cass escape from the ship, they manage to steal a sphere capable of picking up sounds from faraway places and magnifying it. Their geography teacher—later revealed to be Owen—rescues them from the ship and they all head back to land. Unfortunately, there was a search for both Cass and Max-Ernest, as they were reported missing by the school. Owen drops them off at the bus station, and advises them to return home. Instead, Cass and Max-Ernest take the bus to the headquarters of the Terces Society.

Cass and Max-Ernest finally meet Pietro in person, and they are also introduced to the rest of the society members. Pietro surprises everyone by assigning Cass and Max-Ernest to find out all they can about the homunculus, as they were able to acquire the Sound Prism. Eager to prove themselves useful, the duo try their level best to complete their task.

Sometime later, Cass and Max-Ernest have an argument, which made them momentarily dissolve their partnership. While Cass tries using the Sound Prism to call for the Homunculus, she discovers a birth certificate of an unknown girl. Though she now suspects her real identity and origins, Cass remains focused on the task at hand. Meanwhile, Max-Ernest stumbles upon some relevant documents about the Homunculus in a gift Pietro sent him, and decides to pass them to Cass out of courtesy. The two later reconcile, and figure out where to find the Homunculus.

Cass, Max-Ernest and Yo-Yoji proceed to go on a hiking trip with Cass’s grandparents, though only Cass and Max-Ernest are privy to the real reason why they had to go camping in that precise location. At night, Cass and Max-Ernest try to use the Sound Prism once again, but Yo-Yoji catches them in the act. Cass and Max-Ernest are surprised that Yo-Yoji didn’t think much of the matter, even after they told the Japanese boy all about the Terces Society and the Midnight Sun. They are all shocked to see the homunculus arrive, but they did not get a chance to properly speak with Mr. Cabbage Face as Cass’ grandparents had woken up.

After tracking down the homunculus to his lair, they persuade him come to the headquarters of the Terces Society. Mr. Cabbage Face begrudgingly agrees, and they sneak him back inside Max-Ernest’s bag. Unfortunately for the three of them, upon entering the main location of the Terces Society they realized that Mr. Cabbage Face had vanished, presumably fed up with the lot of them. Instead of being disappointed, Pietro encourages them to try harder to find the homunculus. Cass and Max-Ernest are also stunned to find out that Yo-Yoji was actually part of the Terces Society all along, and this relevation makes Max-Ernest stop being hostile towards Yo-Yoji.

After going on an excursion with their science teacher, the two are tricked by Dr. L after receiving a note from Pietro saying he will meet them on a ship, from which they barely escape. After finding out their teacher is really Owen, the accent changing member of the Terces Society, they are introduced to the great magician himself, Pietro, who gives them a mission: find the homunculus before the Midnight Sun does. Max-Ernest also finds out that 'Terces' is "secret" backwards. Cass is grounded when she returns home, because she was missing for too long. While on the Midnight Sun ship, Cass and Max-Ernest discover a strange ball, which enables her to hear all types of sounds by putting it to her ear and makes wonderful music when held carefully. Cass also discovers a birth certificate. The name is unrecognizable, thus making Cass wonder if she was the wrong girl the Terces Society wanted. She ignores it, even though it pains her, and continues her mission.

This time teaming up with a new classmate named Yo-Yoji as well as Max-Ernest, the three need to escape the grasp of their parents, and find the alchemist's grave... but Dr. L and Ms. Mauvais have other plans.