The book details the adventures of Artemis Entreri the assassin and Jarlaxle the drow, formerly of House Baenre, with two new companions: the ghost of a powerful lich called the Witch-King, and an oath-bound knight.

Jarlaxle and Entreri join forces with a group of adventurers, including Commander Ellery, a legendary hero Mariabronne the Rover, assassins Athrogate and Canthan, a half-elf warrior Calihye, and half-orcs Arrayan and Olgerkhan.

As with the original Castle Perilous, the citadel's magic creates an endless supply of gargoyles, who begin to attack the heroes, as well as the poorly defended town of Palishchuk, where Calihye and another injured member of their party are nestled.

A fight promptly ensues, although Jarlaxle seems reluctant to kill her, as they have been lovers for some time and the opportunistic mercenary would always prefer to bed women than slay them, but Entreri shows up and mortally wounds her with his jeweled dagger.

A reviewer from Publishers Weekly comments: "Salvatore keeps the action hopping as the duo use every trick in their repertoire to achieve their goal—finding magical treasure hidden by the long-dead Witch-King.

"[2] Pat Ferrara from mania.com comments: "The second book of arguably the coolest Forgotten Realms literary spin-off to date, Promise of the Witch-King continues the Sellswords Series without skipping a beat.

Tightly knit plotlines, absurd yet memorable and engaging characters, and hellishly fast-paced storytelling culminate in a wild melee of swords and sorcery led by the master himself.