Ghost Light (World of the Ghosts short story)

Caina Amalas is a nightfighter of the Ghosts, one of the Emperor's elite spies and assassins. Summoned to the aid of a desperate merchant, Caina finds herself facing an assassin more deadly than any she has ever fought.

An assassin who harvests the souls of his victims.

And unless Caina is clever, she will become his latest victim...