THE SIGN OF FOUR

A Sherlock Holmes classic is supplemented with essays and addenda.

The 1890 tale was Conan Doyle’s second Holmes novel. The brief and brisk adventure encompasses stolen treasure, the Indian Rebellion of 1857, a chase scene on the Thames, a love story and, of course, the cunning powers of deduction of Holmes himself. (The novel’s first chapter also depicts Holmes’ infamous affinity for cocaine.) The details of the rebellion—and England’s relationship with India in general—are complex, so the app’s sidebar notes on relatively obscure terms and places are handy, as are casual essays on the East India Company and Doyle’s life and translations of Holmes’ French or German bons mots. Accessing the supplementary info is intuitive, and the book reads well in the format. The downside is that the quality of the new material is often erratic. The app’s makers were clearly inspired by the spate of recent Holmes film and TV adaptations, but the essays on them often feel puffy and only casually proofread. Forcing readers to Amazon.com pages where they can order DVDs of Elementary or Holmes films only bolsters the off-putting feel. And often, the new material is sensibly chosen but poorly refined: It’s one thing to include a definition of plaster of Paris, another to needlessly describe the chemical process by which it’s made; an 1857 article by Karl Marx on the rebellion comes with no context on Marx, the genesis of the piece or how it directly relates to the novel at hand.

The app has some visual appeal and usefulness to newcomers to Holmes, but it shouldn’t be confused for a serious critical edition. (Requires iOS 6 and above.)