Teen Sherlock battles a monstrous adversary on a mission to Ireland with his brilliant brother, Mycroft. Young Sherlock is thrown into a tangled web involving a spiritualist whose powers have attracted the attention of governments around the world. At the castle where the medium is demonstrating his gift, Sherlock finds a household in turmoil. Servants and some of the guests are frightened but who--or what?--has terrified them so much that nobody will speak out? Young Sherlock must bring all his powers of deduction to bear in unraveling his greatest mystery yet.