Two for One by Barry Day

A hallucination of Sherlock Holmes helps hardboiled PI Jack Watson solve a perplexing case in this unique take on Sir Arthur Conan Doyle's legendary detective.
In the city of Los Angeles, there's no private detective quite like Jack Watson. A tough-as-nails gumshoe, he's made a reputation as the kind of sleuth who will take any case, no matter how sleazy or small. He's in the middle of a particularly nasty divorce investigation when his client's mistress sees fit to club Watson on the back of the head with an iron. When he comes to, he's in the hospital looking at Sherlock Holmes.
Holmes is translucent and floating slightly above the floor—a figment of Watson's imagination that has come to transform a medie detective into a great one. Hired by the notorious Hollywood producer Osgood Kane, Watson is about to stumble onto a truly baffling case, the sort only Holmes can solve. They're thousands of miles from Baker Street, and a lifetime away from the Victorian era, but when Watson's brawn teams up with Holmes's brain, the game is afoot once again.
Written by legendary Holmes expert Barry Day, whose Sherlock Holmes: In His Own Words and in the Words of Those Who Knew Him is the quintessential biography of the great sleuth, this is an adventure that even Sir Arthur Conan Doyle couldn't have dreamed up. Witty, exciting, and irresistibly fun, Two for One bridges the gap between the modern mystery and history's greatest private eye.