Without Remorse takes place in 1972-73 and has two parallel stories - one in Baltimore and one in Vietnam. John Kelly/John Clark is involved in both story lines; although, most of the focus in on Baltimore.
The character of Kelly/Clark is well drawn by Clancy with a convincing backstory along with a development of his character through tragedies and his response to them. The title of the book applies to Kelly/Clark's response to those tragedies.
Having read plenty of thrillers from Vince Flynn to David Baldacci, this story of Clancy is not an old yarn and contains many surprises. However, the one plot twist in the novel is telegraphed early on.
Overall I recommend this novel as a great summer read. Although written after several other Jack Ryan novels it is the first in the chronology of the Ryan universe. If you find the novel in your travels, then grab it and give it a go.