After five beguiling mysteries featuring redoubtable, stolid police detective Brendan Moran, “The Enemy Inside” is an interlude, a terse, thrilling novella that allows author Scott Hunter to explore both Moran’s past in the Irish Troubles and his moral capacity. The story rattles into action with a suicidal ex-soldier intruding into Moran’s life, bringing accusations of tragic past misconduct to bear with escalating violence. Seamlessly blending the past and present, Hunter sets up a tableau of detective digging and home invasion, but then ups the ante with two astonishing climaxes and a final fraught decision. This is no-holds-barred plotting that stuns. Moran is a bear of a justice-seeker well suited to our heaving 2020s and this series is destined for greatness.