The usurer had a phony doctor listen to Admiral's heart.
"
"The doctor was a rogue too. I didn't like the look
of him at the time."

"Arcades ambo."

I found a site which says the above phrase means "Both were rascals" - it fits.

A french site has this:
Arcadiens tous deux.
Virgile (égl. VII) représente deux bergers, Thyrsis et Corydon, se préparant au combat de la flûte.
Ambo florents azlatibus, Arcades ambo...
(Tous deux jeunes, Arcadiens tous deux...)
Comme l'Arcadie n'était pas moins célèbre par ses ânes (roussin d'Arcadie), on dit quelquefois d'un couple de sots : Arcades ambo, et, en général, de tout couple qui, dans une circonstance donnée, prête à la malice, à la plaisanterie.


M. Capefigue vint à Paris vers 1821, c'est-à-dire à l'époque où y arrivaient MM. Thiers et Mignet, accourus d'Aix-en-Provence pour chercher fortune, comme tant d'autres, dans la grande ville. Tandis que ces deux rivaux, Arcades ambo, mettaient leur talent naissant au service de la cause libérale, M. Capefigue se faisait recevoir élève à l'école des Chartes.

For what it's worth the url is http://www.abnihilo.com/indexredir.htm. However, you may have to look it up yourself once you get there.

Brewers has this:

Arcades Ambo, both fools alike; both “sweet innocents;” both alike eccentric. There is nothing in the character of Corydon and Thyrsis (Virgil’s Eclogue, vii. 4) to justify this disparaging application of the phrase. All Virgil says is that they were both “in the flower of their youth, and both Arcadians, both equal in setting a theme song or capping it epigrammatically;” but as Arcadia was the least intellectual part of Greece, and “Arcadian” came to signify dunce, and hence “Arcades ambo” received its present acceptation.

http://www.bibliomania.com/2/3/174/1111/15786/1/frameset.html

Virgil's Eclogues 7. The source of the quotation: http://makeashorterlink.com/?D274124C6

Judging from Google, Baroness Orczy and Lord Byron both seem to have been rather fond of the phrase. Byron glosses it with the villainous meaning. I don't know how La Baronne uses it.


Bingley

Dear Bingley: I searched for "orczy Arcades ambo" and got this
http://www.classicreader.com/read.php/sid.1/bookid.1809/sec.9/

A chapter is entitled "Arcades ambo" and appears to refer to two characters, Heron and DeBatz, who are hoping to trap the Scarlet Pimpernel. (Dramatic musical flourish)