The occupying force is Russian, the resisters British in this durable thriller by Egleton (A Dying Fall, 2005, etc.), first published in 1972.
Since the Occupation began six years ago, undercover agent David Garnett has been in the business of suborning puppet governments, and he’s good at it. But in guerrilla-fighter years, six is an eternity; weariness has set in, disillusion in its wake. Patriotic fires banked, Garnett feels an undeniable urge to rusticate, and in effect that’s what he’s been doing in a tiny, out-of-the-way Lake District village until he’s rousted, cover blown, with the local cops in hot pursuit. So now, after months of relative safety, Garnett and lover/comrade-in-arms Valerie Dane are on the run—in different directions. Garnett decides reluctantly that he has only one option: to ask help from Vickers, aka the General, the spidery power behind the Resistance. Vickers is amenable. He’ll provide a hidey-hole for Garnett and Dane, but there’s a quid pro quo, of course. Garnett knows Vickers well enough not to be surprised, but the details unsettle him. Six jailed politicos, Resistance VIPs, are about to be transferred from one prison to another. Vickers wants Garnett to mount an operation aimed at breaking them loose so that they can form a Government in Exile in the United States. Fully aware that the scheme is harebrained and the odds against success prohibitive, Garnett signs on anyway; his alternatives range from grim to none. Almost nothing goes right, and a hopelessly porous plan is further undermined by a cowardly betrayal, yet suddenly Garnett and Dane, in the company of the shanghaied six, find themselves just one small step from the promised land.
A spy trying to come in from the cold: not quite as heart-wrenching as le Carré’s, but you'll still care.