And the Moonbeams Kiss the Sea (S02E01)

At first the murders of Reg Chapman, a handy man at the Bodleian Library and gambling addict, and Nell Buckley, a popular Art student, seem unrelated. However, it transpires that Chapmen stole parchment from the library upon which Nell and another student persuaded Philip, a brilliant, autistic young painter, to innocently forge letters by the poet Shelley for the international collectors' market. When both victims, for different reasons, threatened to expose the mastermind behind the scam, they were killed. (iTunes)