No Enemy but Time — Evelyn Anthony

The wife of a prominent British politician returns to Ireland to find her missing half-brother -- and plunges into a hotbed of political unrest and murder
 
The wife of an important British Cabinet minister, Claire Fraser lives the kind of life that fills the society pages. But when the disappearance of her half-brother, Frank Arbuthnot, makes international headlines, she abandons her very public life in London to search for him in her native Ireland.
 
On returning to her homeland, Claire is besieged by memories of a childhood full of innocent adventures and games, family dogs to feed, ponies to ride -- and Frank ever at her side. Her half-brother had always been there, keeping her safe, her dearest and closest ally.
 
And now he's vanished -- kidnapped, possibly murdered. Clare knows she has to find him; Frank needs her now, more than ever.
 
Cross-cutting between past and present, England and the political unrest of strife-torn Ireland, No Enemy but Time is a page-turning thriller as well as a tragic love story.