While not entirely out of the norms of Victorian judicial practice, Lord Chief Justice Cockburn’s summing-up of the evidence in Regina v. Castro, aka Arthur Orton, aka Roger Tichborne was extraordinary for its length and detail, as well as for its narrative and rhetorical force. This article examines Cockburn’s summing-up to the jury, arguing that while it is revealing of nineteenth-century British conceptions of identity, it also uncovers the instability and insufficiency of those conceptions for the juridical determination of identity. Thus the summing-up of evidence, and perhaps the entire Tichborne affair, suggested some of the ways that law, in an age of rapid urbanization and increasing geographical and class mobility, would increasingly require supplementation from extralegal disciplines.