The fourth season of "Sherlock" strays too far from its source material.

Since its 2010 debut, Mark Gattis and Steven Moffat's modern interpretation of Sir Arthur Conan Doyle's classic detective stories about Sherlock Holmes have become a worldwide phenomenon. "Sherlock" has also made superstars of stars Benedict Cumberbatch (Holmes) and Martin Freeman (Dr. John Watson). But in its fourth season, the show is starting to feel less about the detective's casebook and more about their family trees.

If character is story, then Holmes should be illuminated by his deductive work helping solve crimes. The stories in Conan Doyle's canon are procedurals, after all. But over the last two seasons, "Sherlock" has strayed from whodunit's and become far more obsessed with backstory. Holmes family history and Watson's marriage are interesting, but they shouldn't be the main mysteries. It seems almost elementary, but as the show continues it shouldn't stray so far from its classic source material.