What precipitates Charles's decision to return to France in A Tale Of Two Cities?

Charles Darnay, ne Charles Evremonde feels the loadstone pulling
him in Book the Second, Chapter XXIV of A Tale of Two Cities. After the
chateau of the Marquis d'Evremonde is burned by some of the villagers who have witnessed the
callous running over of a boy by the carriage belonging to the Marquis, Monsieru Gabelle, the
collector of rent and taxes has his house surrounded.  He is "summoned ... for personal
conference," but he bars his door, and writes to the nephew of the Marquis, Charles
Darnay/Evremonde.

In a desperate letter, Gabelle writes from the
prison of the Abbaye, Paris, informing Charles that he has been arrested for treason.  Even
though Gabelle has told his captors that he has collected no rents or taxes, they insist that he
has "acted for an emigrant, and where is that emigrant?"  Gabelle begs Charles to return to Paris
"to succor and release me." Declaring that he has been true to Charles, he begs Charles to be
true to him. 

Darnay is "roused to vigorous life by this letter." 
He cannot bear to think that the old and faithful servant should be in such peril; therefore, he
sees no alternative but to return to Paris:

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Yes.  Like the mariner in the old story, wht winds and
streams had driven him within the influence of the Loadstone Rock, and it was drawing him to
itself, and he must go.

Darnay
resolves to go to Paris to clear Gabelle of the charges against him by testifying that he has
ordered that the people be spared their debts, be given what fuel could be saved.  Also, Darnay,
who fears no harm to himself since rejected his own nobility, hopes that he can exert some
influence "to guide this raging Revolution that was running so fearfully wild."  This intention
and the fact that he leaves behind "all that was dear on earth...and floated away for the
Loadstone Rock" suggest that Charles Darnay may come into conflict with the forces of
fate.