At this point in A Tale of Two Cities, because he is "a notable sufferer under the overthrown system" Dr. Manette has been allowed to attend the prisoners of the Revolution; and, in so doing, he has grown resolute. Now "his suffering was strength and power," and he feels that he can be instrumental in effecting the release of his son-in law. When he speaks to Mr. Lorry, who is surprised as such purpose and strength in Manette, the doctor tells him,
"It all tended to a good end, my friend; it was not mere waste and ruin. As my beloved child was helpful in restoring me to myself, I will be helpful now in restoring the dearest part of herself to her; by the aid of Heaven I will do it!”
Using his influence as the "Bastille Captive," Dr. Manette has even become physician for Laforce, so he sees Charles every day. Mr. Lorry observes that Manette's pride has returned to him now that he has a purpose. Among the terrors of the guillotine, with death all around him, the brave doctor walked, "confident in his power, cautiously persistent in his end." Manette tries to get Darnay released, but for some reason his release was rescinded. Despite his futile attemps to arrange the release of Darnay, Dr. Manette still is not suspected or brought in for questioning; he moves freely, almost like a spirit.
It is surprising that, considering the way in which Dr. Manette spends so much of the novel showing his fragility and vulnerability to his madness, having spent so much of his time locked up, that at this point of crisis in the novel, he should suddenly find new strength. And yet this is precisely what happens. In this chapter, as Dr. Manette relays to Jarvis Lorry the full horrors of what he has seen, Jarvis Lorry himself is concerned about Dr. Manette's health and whether a relapse might occur. Yet, at the same time, we are told that Jarvis Lorry had "never known him in his present character." Note what we are told regarding Dr. Manette's character at this time:
For the first time he felt that in that sharp fire, he had slowly forged the iron which could break the prison door of his daughter's husband, and deliver him...
Thus it is that Dr. Manette feels that the years of suffering he had endured have helped him gain an inner strength that he can now use to save his son-in-law. This explains why he has "kindled eyes, the resolute face..." In this time of great trial, it appears Dr. Manette has been revitalised and re-energised and that he is full of energy to do what needs to be done to secure the release of Charles Darnay.