How does Dickens use suspense in his account of Carton's plan with Barsad?"A Tale of Two Cities" by Charles Dickens

In Book the Third of "A Tale of Two Cities," Miss Pross is on her way with Jerry Cruncher as "purveyors" for the Darnay family.  Charles Darnay has been set free, but is again charged by "Saint-Antoine" and is returned to the Conciergerie.  As Miss Pross recognizes her brother Solomon, so, too, does Jerry recognize him.  However, he knows this man to be John Barsad, from the trial of Darnay at the Old Baily.  Coming out of the shadows, Sydney Carton reaffirms this identification. 

Then, Carton tells Solomon/Barsad that he has been observed going into the prison of the Conciergerie.  And, as Carton has observed Barsad, he has thought of a "purpose."  But he cannot explain it on the street, he tells Barsad; so, he asks the spy to accompany him to Tellson's Bank.  Because of the look Carton gives him, Barsad agrees to accompany him. At the bank, Mr. Lorry,too recognizes Barsad.  Sydney, having informed Mr. Lorry of Darnay's second arrest, tells Barsad that he "proposes...to win" is a friend. That friend is Mr. Barsad.  Barsad counters this proposal:  "You need have good cards, sir." 

Carton does, indeed, have "good cards." He releases his information on Barsad:

Mr. Barsad, now in the employ of the republican French government, was formerly in the employ of the aritocratic Englsih government, the enemy of France and freedom.  That's an excellent card....I play my Ace, Denunciation of Mr. Barsad to the nearest Section Committee.  Look over your hand, Mr. Barsad, and see what you have.  Don't hurry.

Barsad has been a double-spy, an informer first for the French, and now for the English.  The apprehension that he is not safe comes upon Barsad as he envisions Mme. DeFarge knitting her register of names. "He foresaw that the dreadful woman of whose unrelenting character he had seen many proofs, would produce against him that fatal register, and would quash his last chance of life.

Still resuming his air of contemplating cards, Carton reveals that he understands the third identity of Barsad:  Roger Cly, the very man who has feigned his death in England.  Now, Carton has his man as he described a conversation that Roger Cly has had with an officer in the prison: 

A plot in the prisons, of the foreigner against the Republic.  A strong card...A Guillotine card!

Charles Dickens does not reveal the plan here, only that there is one, an interesting one, at that.  The reader perceives here how all the minor plots will play into the main plot as all of the characters from London are now in St. Antoine--a tale of two cities, indeed.