In Janáček's opera The Makropulos Case, the operagoer must accept a single premise of implausible fantasy: from then on, the action flows inexorably and logically to its conclusion. It's a device used by a great deal of fantasy literature, from the low-brow of The Day of the Triffids to the high-brow of Janáček's compatriot Kafka's Metamorphosis.
