There is nothing more deceptive than an obvious fact.
—“The Boscombe Valley Mystery”
An important distinction can be made, when reading the Holmes canon, between the cases in which Holmes helps a client directly or when he is cajoled into assisting the police inspectors of Scotland Yard. Without exception, Holmes endeavors to serve his clients well, and, as with Mr. Wilson in the “Red-Headed League,” to protect them. When brought in on a police investigation, Holmes displays the same skill, albeit raised to an almost competitive level, but there is also an increase in acrimony or ill feeling. Watson repeatedly endorses being somewhat resentful for Holmes serving simply as an instrument for solving the case, yet receiving none of the credit. Moreover, Holmes himself is critical of the methods deployed by Scotland Yard, as they are often no match for his own deductive abilities and techniques.
As such, and as he is no mere extension of the police force, Holmes feels no similar duty to protect the inspectors he helps, and, in fact, many of the Scotland Yard detectives, including Inspectors Gregson and Lestrade (from A Study in Scarlet) and Inspector Althelney Jones (from A Sign of Four) follow incorrect assumptions, make erroneous arrests, and otherwise bungle their own cases without much more than a snide remark from Holmes. Thus, Holmes may assist, or even allow the inspectors to take the credit for solving his cases, but he may not protect them. In a few cases, this duty to protect amounts to keeping secrets, either from clients or the police, or, as in the case of “The Boscombe Valley Mystery,” which is unique in being both a “client” consultation and a collaboration with Scotland Yard, pitting the two against one another, and keeping the secret at the heart of the mystery to himself.
As with “A Case of Identity,” Holmes is not above keeping information he regards as potentially damaging from his client. In “The Boscombe Valley Mystery,” this particular scruple is considerably expanded and extended to keeping information from the police and, in fact, instituting a ‘cover-up’ of far more serious crimes out of a sense of moral obligation to his adopted “client” and their family, although Holmes’ services were in fact retained by Inspector Lestrade. While the idea of secret-keeping is central to the Holmes canon, as it would be for any detective to engender trust in his or her clients, Holmes and Watson alike display a far more acute sense of preservation and protection of both life, liberty and reputation in “Boscombe” than was common in Victorian society.