If exasperated, Cavaillon might refuse to divulge who this person was,
who after all might not bear the name "Gypsy" given by the cashier. And,
even if he did answer his questions, would he not lie?

After a mature reflection, Fanferlot decided that it would be
superfluous to ask for a secret when it could be surprised. To quietly
follow Cavaillon, and keep close watch on him until he caught him in the
very act of handing over the letter, was but play for the detective.

This method of proceeding, moreover, was much more in keeping with the
character of Fanferlot, who, being naturally soft and stealthy, deemed
it due to his profession to avoid all disturbance or anything resembling
evidence.

Fanferlot's plan was settled when he reached the vestibule.

He began talking with an office-boy, and, after a few apparently idle
questions, had discovered that the Fauvel bank had no outlet on the Rue
de la Victoire, and that consequently all the clerks were obliged to
pass in and out through the main entrance on the Rue de Provence.

From this moment the task he had undertaken no longer presented a shadow
of difficulty. He rapidly crossed the street, and took up his position
under a gateway.

His post of observation was admirably chosen; not only could he see
everyone who entered and came out of the bank, but also commanded a view
of all the windows, and by standing on tiptoe could look through the
grating, and see Cavaillon bending over his desk.