The story concerns a magic potion that causes the person to whom it is administered to become what he or she has pretended to be. It is similar to several "magic lozenge" plots that Gilbert had proposed to the composer Arthur Sullivan, but that Sullivan had rejected, earlier in their careers.
In this narrative, there's a magic potion that alters the individual consuming it into someone else they pretended to be. This plot bears resemblance to some "magic lozenge" ideas Gilbert presented to Arthur Sullivan, though Sullivan rejected these earlier in their professional lives.