Burn

The demon Lucrecia accompanies her mistress to a remote castle to evaluate a powerful duke. He is suspected of dark magic and may be plotting to steal his brother's throne. Lucy is shocked to discover that the duke has hired her erstwhile lover, the sorcerer Jacob, to vouch for his purity. Both Lucy and Jacob have agendas of their own at the duke's castle. They may need to put past quarrels aside if they want to leave alive.

This short novel is related to The Incubus series, but can also be read as a stand-alone.