The "very short introductions" may be what you are looking for. They cover topics in philosophy. Here is Wikipedia's description:
Very Short Introductions (VSI) are a book series published by the Oxford University Press (OUP). The books are concise introductions to particular subjects, intended for a general audience but written by experts. Most are under 200 pages long. While authors may present personal viewpoints, the books are meant to be "balanced and complete" as well as thought provoking.
Two other sources to keep in mind are the Stanford Encyclopedia of Philosophy and the Internet Encyclopedia of Philosophy.
Although these are not all in one book, they are short and give you exposure to more than one author.
Wikipedia contributors. (2019, August 22). Very Short Introductions. In Wikipedia, The Free Encyclopedia. Retrieved 14:48, September 10, 2019, from https://en.wikipedia.org/w/index.php?title=Very_Short_Introductions&oldid=912030519