FAITH by Len Deighton (HarperCollins: $24; 384 pp.) Nice trick, immortality. The way the doughty Len Deighton has arranged it, all you need is a typewriter and a few loose ends. With imagination, scrupulous attention to the punctilio, the manners and mores of the British Secret Intelligence Service (SIS), a chorus of grace notes and a rare ability to keep us caring, Deighton serves up his seventh Samson with absolutely no diminution of style. It’s Deighton’s way and his strength: Even his minor players have a pedigree.) Anyway, for “Faith,” Samson, dogged, obstinate and all-too-human as usual, is brought back from semi-disgrace in California to locate and reel in one “Verdi,” a KGB defector who promises SIS access to his Berlin headquarters’ computer system. Samson journeys to Magdeburg (in East Germany), only to find Verdi harboring a bullet in his brain. Deighton says in an “Author’s Note” that “Faith” may be read “without reference to the other stories.” A better suggestion: Buy paperbacks of the first seven of the saga.