Final answer:
Darnay's return to France is likely due to the political turmoil after Napoleon's exile and the reinstatement of the Bourbon monarchy. Widespread discontent and shifts in power during that time may have influenced his decision.
Step-by-step explanation:
Why does Darnay decide to return to France? Looking at the context provided, we can infer that Darnay's decision to return to France is influenced by the events unfolding during that turbulent period in French history. After Napoleon's exile, the Bourbon monarchy was restored to power with Louis XVIII as the king. Due to a combination of ineptitude in governance by the new king, the hardships faced by the common people, and the return of the émigrés claiming back their privileges, there was widespread discontent.
This environment eventually facilitated Napoleon's return, which might have impacted Darnay's decision. He likely saw an opportunity or felt an obligation related to the shifting political landscape and the revolutionary spirit that was emerging once more in France.