Recommendation: the novel 'Spur', by Phil Geusz

Our protagonist has accepted being cursed into the shape of a horse, taking the place of a wealthy man in exchange for luxuries and lots of monthly cash. The wealthy man dies - and to his horror, our hero finds he is still a horse. Events escalate, secrets are revealed, personal growth happens. While not exactly dedicated to Bayesianism or even just rationality, the climax involves the expression of a sentiment familiar to any reader of HPMoR who's gotten to the bits about dementors, and seems to express it quite well in terms readers more familiar with fantasy than science-fiction can appreciate, which could form a stepping-stone to dealing with the idea of existential risks in the real world.

Discovered through this review. Available through Lulu or Amazon for $15, or as a PDF or HTML ebook for $6.