Try Second Chances. It's a novel for the Frostgrave wargame where wizards hire bands of henchmen to explore the ancient ruined city of Fellstad to loot it's magical treasures.

The novel itself is about two sisters. One a gifted chronomancer, the other... bereft of magical gifts. The second sister stupidly makes a deal with a demon. It'll give her magical powers but each time she casts a spell, she is one step closer to losing control of her body to the demon.

When they hear a rumour about the location of an artefact in Fellstad that could break this deal, the sisters decide to venture into the lethal ruins once more to find this artefact.

Meanwhile they're being hounded by their former mentor, a powerful illusionist. And a liche is holding the artefact while working out it's own plot.