Death in a Half Foreign Country

When John Mordred leaves MI7, marries the woman he loves, and settles down to a relatively humdrum lifestyle, it ought to be a brave new start. But he and his wife have formerly been top-level spies, and they find the readjustment harder than they anticipated.
Unfortunately, there's also a limit to how far they can walk away. Especially when any number of foreign intelligence agencies have hostile eyes on them. They were once two of Britain's best assets; they're currently untethered from central control.
And actually, come to think if it, this is an excellent time to put an assassin on their tail. Get rid of them both, once and for all.