Perhaps the most attractive aspect of "The Third Secret" lies in the way it depicts the rivalries between the police and the Carabinieri. Initially it seems as if the two will never co-exist, as Montalbano (Michele Riondino) becomes involved in a complicated case involving the death of an Albanian builder (Andry Maslonkin) who turns out to be an under-cover police officer. Once Montalbano learns that it is perhaps the Carabinieri boss's last case, as he will die soon owing to a brain tumor, his attitude relents, and the two of them manage to clear up the case. Until that point, however, it seems that too many detectives might spoil the broth, so to speak.
Gianluca Maria Tavarelli's production also complicates the relationship between Montalbano and the luckless Catarella (Fabrizio Pizzuto). The episode opens with a dream sequence where Montalbano imagines himself in a shoot-out, and Catarella ends up being killed. The inspector's guilt - even if only in a dream-sequence - colors his future dealings with Catarella, as he lets him into a series of secrets (hence the "third secret" of the episode's title). In truth none of the secrets are very significant, but Catarella nonetheless shows devotion beyond the call of duty. Eventually the two men become involved in a shoot-out, but Catarella emerges unscathed.
The episode contains two distinct plots, one involving the Mafia and a corrupt builder, the other a young Tunisian woman (Perla Giordano) trying to escape her pimp and get married. This latter plot is resolved in a dramatic sequence right at the end, but on the way director Tavarelli manages to make some trenchant observations about the ways in which immigrants from so-called "Third World" nations are often abused. In light of current affairs, with mass immigration to Europe from Syria and Afghanistan, the plot becomes even more pertinent.
To be honest, Michele Riondino is both facially and bodily very different from the older Montalbano; it is hard to believe that the characters are designated to be one and the same. Viewed on its own terms as a stand-alone detective thriller, however, "The Third Secret" remains riveting entertainment.