Volume four of Black Butler is a little lighter in tone than volume three ended up being. Ciel investigates a series of mysterious attacks on “Anglo Indians” (British colonists returning from India.) During the investigation, Ciel and Sebastian run into Prince Soma, the 26th child of the raja of Bengal. The prince is searching for one of his servants, a woman named Mina, who had allegedly been kidnapped by a British noble.
After an altercation involving a group of Indian immigrants, Soma and his servant Agni invite themselves into Ciel’s home to petition him for aid. (Also present is Lau who is only slightly less aggravating to Ciel than Prince Soma and his servant are.) Ciel ends up being very impressed by Agni who is apparently the Platonic Ideal of a butler. He is in every way Sebastian’s equal, the Platonic Ideal of “butler,” and he appears to be Sebastian’s superior in at least one regard: he is able to manage the servants, something Sebastian is not able to do. (My “headcanon” is that this is partly because Sebastian wants to make his own work look that much more effective by contrast.)
Ciel does not initially want to help Soma, but he finds himself drawn in due to Soma’s persistence. It is eventually revealed that Agni is responsible for the attacks, which have been committed at the behest of an English noble named West, who is attempting to obtain a “Royal Warrant” for his business. The noble is attempting to remove the competition for a curry making contest where Agni will be participating. It also turns out that West is responsible for the disappearance of Soma’s servant Mina.
Soma is devastated by this betrayal and does a great deal of acting out about it. This results in Sebastian ripping Soma up one side and down the other. He points out that Soma has done nothing to deserve service, that everything he has is from his father, and that Soma is a spoiled brat. Ciel interrupts the harangue, stating that he might have been like Soma if circumstances had been otherwise. (Ciel honestly seems to believe this but I have my doubts.)
This volume goes into a little more detail about what happened to Ciel after his parents were murdered. Ciel was apparently sold to a group of occultists, who abused him and then made him the featured event in one of their rituals. The occultists were able to raise a demon that turned out to be more interested in the sacrifice than the celebrants. (Interestingly, the demon speaks as if Ciel were the one who summoned him, and not the occultists. I am torn over whether this was the literal truth, or if this was just manipulation to ensure that Ciel would make a contract with him.)
Soma apologizes for being overly distraught and Ciel reveals that he suspects that Agni is working with West under duress, and that Agni is in fact still loyal to Soma. He also states that he plans on having Sebastian enter the contest. (Ciel claims that he was planning on creating a culinary line for his company.) Soma doubts that this plan will work, because Agni excels at everything, and that includes cooking. We end the volume with Sebastian accepting the challenge. In the next volume, Sebastian learns how to make curry, and we get a hint of the next arc.