Our Universe is majestic, magnificent in its splendour and deeply mysterious at the same time. Throughout this book, we shall try to act as Cosmic Detectives. Through careful observation of some very elementary clues scattered across the sky, we try to gradually discover some of the deepest and darkest secrets or mysteries of the Universe. From our familiar shoreline on the Earth, we dare to venture into the harrowing depths of vast unknown Cosmic abyss. Believe me, it will be a fascinating journey indeed!