After the death of her beloved twin brother, Felix, and the break up with her long-time lover, Nathan, Greta Wells embarks on a radical psychiatric treatment to alleviate her suffocating depression. But the treatment has unexpected effects, and Greta finds herself transported to the lives she might have had if she'd been born in a different era.
Severity reflects intensity, not value — “central theme” means a warning is a core part of the book, not that the book is bad.