Sentinels from Space
David Raven, of course, is no ordinary hero — the unusually beautiful Leina, no ordinary heroine. Together they form a team, sharing an awesome secret. With incredible powers undreamt of by single mortals, they voluntarily take upon themselves the guardianship of humanity.

They are the Sentinels.

Together they watch the sky, lying back, alert faces to the stars. Out, far above them, deep into space they feel the pulse of the Milky Way which stretches like a gauze veil across the zenith. Among thousands of worlds they search for one significant gleam in the dark. The stars blaze down, but the world around them is deep and dark, bitterly dark. And in that darkness, somewhere, are the black ships of the Denebs.
science fiction, British science fiction
Eric Frank Russell
English science fiction writer