Keys to the Kingdom. Bk.6. Wonderful Saturday

Arthur Penchaligon managed to take away five keys from their immortal keepers, but taking possession of the sixth key is not an easy task. Excellent Saturday is not just one of the proxies, she is the oldest resident and the most powerful sorceress in the house. And everything that is now happening around the legal heir seems to be part of the plan, the execution of which she has been observing for ten thousand years.
Arthur is besieged from all sides: they attacked his hometown, the house collapses, and the allies are absolutely unreliable. The heir simply needs to penetrate the impregnable upper house, because only the strength of the keys can interfere with what is happening. But even if Arthur manages to take possession of the sixth key, is it enough to confront the witchcraft of the Sabbath and prevent her from completely seizing power?