The characters are wasps from the devastated nest of Ys’drktha. The other survivors from the cataclysm are being held and tortured in the pits of the neighbouring Ak’thaan nest, being slowly dismembered and eaten by drone wasps or fed to the writhing masses of larvae.
In the harbour of a major city a large and terrifying ship made of human nails docks. Nobody seems to inhabit this ominous vessel, someone needs to go on board and unveil the mystery. In comes the PCs.