What is the significance that Charles Darnay is placed under escort as soon as he arrived to France in Book 3, Chapter 1 of A Tale of Two Cities?
Let us remember the rather momentous decision that Charles Darnay has made. In a time of revolution, when he has definite aristocratic links, even though he has tried to dispense with them, he chooses to return to France and go to Paris to try and save the life of one of his former servants. The dangerous and risky enterprise this is is highlighted in a number of ways, but in this first chapter of the final book, we see how the grim ending is foreshadowed through the immediate hostility Charles Darnay, formerly known as Everemonde, faces. Note how the functionary greets him when he is woken at night by a force of soldiers and officials:
"Emigrant," said the funcitonary, "I am goign to send you to Paris, under an escort."
The title of being an "Emigrant," combined with the way that he is insulted just a couple of lines later as being an "Aristocrat," clearly hints that Darnay is going to face difficulties. Indeed, you could argue that this foreshadows the way in which he will be tried and accused, and the death that he is fortunate enough to escape. It is an incredibly dangerous place for aristocrats, and Darnay has just placed himself in immense danger. Note the way that this also increases the tension at this crucial stage in the novel as we wonder what will happen to Darnay.