I'd definitely give it 3 1/2 stars if I could. Great read and a very clever, even unique (don't get to say that often) premise. Winston Churchill described his depression as a "black dog," and in this book, Rebecca Hunt makes depression a huge, monstrous, talking, bothersome black dog who hounds those he's assigned to visit.
In the novel, Churchill is on the eve of retiring from his 64 years of public service, and Black Pat is busy torturing him. His only breaks come when the dog is working on young librarian Esther, who is experiencing the second anniversary of her husband's death. Churchill would like to rid himself of the dog's involvement in his life, but as his momentous occasion briefly intersects with Esther's difficult day, he sees that he has an opportunity to encourage someone else to be rid of the dog. Depression may have settled in permanently for one character, but it might not have to be an ongoing presence for another, if she has the strength to combat it.
Hunt's novel is a clever and intriguing examination of depression and how it can settle into one's life. The conversations Esther and Churchill have with Black Pat are insightful and fascinating, giving form to what is usually shapeless. The dog is persuasive, intelligent and derisive. But, as the book eventually shows, however insistent Mr. Chartwell is, there is hope.

Read my full review, including a rating for content, at RatedReads.com: https://ratedreads.com/mr-chartwell-clean-fiction-book-review/