“Republic Under Siege: Threat from Within” is a sci-fi thriller written by Michael J. Brook. The book is basically the second part of ‘The Wars of the New Humanity Series’. The first part, which features a book called 'Republic Falling: Advent of a New Dawn' tells the story of humanity being partitioned between two worlds (Eden and Satellite One) and the violent war that ensued. On the other hand, this book features life after that war and has a different tone. After the war, an oppressive government system took hold in the colonies of satellite one. Life in these colonies was substandard. Lottery beneficiaries were harvested and transplanted to Eden. Akane Sugimori is an interesting character used by the author to tell the story of the fate that awaited these “lottery beneficiaries” on their arrival to Eden as immigrants. Akane, faced with marginalization, and discrimination; opted to be part of, and eventually became a member of a secret social organization called RISE which was a private organization of social activists fighting for colony and immigrant equality. On the other side of Eden, we find the opposite ideology, PURISM. Purists through violence and election meddling sought to keep the status quo. Purists fought to keep the oppressive government system in place. The assassination of most of Akane’s RISE family was "the straw that broke the camel's back". Akane, burning with the heat of vengeance, disappeared on a revenge mission. In this book, the writer strives to show a vivid picture of the marginalization and discrimination suffered by the “inferior class” and their struggle to break free. In my opinion, the writer excels in describing the resilience of the oppressed. I particularly enjoyed the flow and trend of the story. I find the book to be highly engaging because the author does a pretty good job of telling the background story of Akane through chapter interludes. This helps the reader to better understand the most recent events. However, I am a little saddened in the concluding part of the book because I do not feel a sense of complete victory for the oppressed. In conclusion, “Republic Under Siege: Threat from Within” is one of the best sci-thrillers that I have read. It is a well-written and awesome book full of action and unpredictability. I recommend others to buy a copy and read this compelling fiction. Due to the high number of crime scenes, this book will be appropriate for adults and It is available on Amazon.