This installment of the Capital Mysteries series, 'Who Broke Lincoln's Thumb?', offers a classic early chapter book mystery for young readers. Protagonists KC and Marshall are presented with a clear problem: a damaged national monument, the Lincoln Memorial. Their quest to uncover the culprit and ensure the statue's repair before a public event drives the narrative. The book handles the mystery in a straightforward, age-appropriate manner, focusing on observation, deduction, and teamwork rather than suspense or danger. The emotional arc is one of mild concern and determination, leading to a satisfying resolution. This book is specifically for early elementary children, particularly those who enjoy solving puzzles and are drawn to a sense of adventure in a real-world setting. A parent might reach for this when their child shows an interest in mysteries, is learning about American history or government, or is looking for a new, reliable chapter book series. There are no sensitive topics requiring parent preparation; the story is gentle and engaging. Younger readers (6-7) will enjoy it as a read-aloud or for guided independent reading, while older early elementary children (8-9) will likely devour it independently. What sets this apart from other early mysteries is its unique Washington D.C. setting, which subtly introduces children to national landmarks and a sense of civic responsibility, making it both entertaining and mildly educational.