Marriage and Murder

Five years ago, Henry, Lord Glossup, was suspected of murdering his late wife. Although he was exonerated and the true murderer caught, Henry has been accused of murdering a lady again, in the same fashion. He appeals to Barnaby and Penelope for help, as does Stokes who, having been the inspector in charge of the previous case, is tasked with solving the current one. The investigators soon establish that the evidence implicating Henry is flimsy and circumstantial, and his alibi is easily verified. But that leaves them, along with the sister of the deceased, to unravel the tangled puzzle of who strangled Viola Huntingdon and was it the secret admirer she referred to only as "H"?