I am currently studying for my RYA yachtmaster theory course and was unable to find a book that simply described the COLREGS. My tutor recommended this one because the regs are laid out as they are in law.
Written relatively simply, it is easy to understand, and well enough to play the discribed scenarios and situations through your mind, which is important.
It covers: Steering and sailing rules, Lights and Shapes, Sound and light signals and even the technical details and requirements of the Lights, Shapes and Sound equipment.
There is another similar, more expensive version of this book, which is full of questions and scenarios to test you. This one though, just covers the basic rules, and is pocket sized, which is great to keep in your pocket, wheelhouse or nav table.