Every Srivaishnava obtains three rahasyas known as Rahasya Trayam from their acharya. The work known as Mumukshuppadi details the meanings of those three rahasyas.
Manavala Mamunigal has written a lucid commentary for it.
This book is an attempt to translate that commentary into English. It should be used as a guide and not as a replacment to learning it from an acharya.
Mumukshuppadi has three parts - one each for the meanings of the three rahasyas. Following that, this book is also being released in three parts.
The first part deals with Thirumantram.