This story is a sequel to The Strangers in Ponyville
Second Glance is a Crown Investigator: His job is to look into "matters of interest" for the Princesses. While the hunt for changelings continues, three years after their attack, and is very much a matter of interest, it is not the only matter of interest. Or, for Second Glance, not even a very important one.
At least, not compared to the hunt for the elusive and enigmatic Prince of Ponyton, who may well prove more dangerous than even Queen Chrysalis if he remains free.