In the Company of Ghosts (Book 1 of In the Company of Ghosts) by Stephen Hunt
Approx. 35,730 words.
Published on July 22, 2012.
Agatha Witchley used to be a spy in the Cold War, but now she's locked up in the UK's premier maximum-security mental institution. She believes that the ghosts of the celebrity dead visit her padded cell and whisper the world's secrets in her ears. Which is a big problem for the British government, because she's the only one who can help them when an American billionaire is murdered in London.