Dioclesian is the tale of a simple Roman private, Diocles, who fulfils the prophecy of Delphia (a prophetess, and hence Dioclesian's alternative title) that one day he will become emperor. In the meantime, Diocles avenges the slaying of the previous emperor and becomes a hero. With ambitions realized he discovers the he has over-played his hand by responding to Princess Aurelia's advances in the place of a nice homely girl called Drusilla, whom he had agreed to marry. The prophetess, who happens to be Drusilla's aunt, plans his come-uppance before he realizes the emptiness of his aspirations, abdicates and returns to nature and Drusilla. It is good to know the story of Purcell's first major theatre success, though not essential since this hotch-potch adaptation of older plays impinges little on the music and, moreover, none of the protagonists sings a note. Yet this production at Dorset Garden in 1690, with all the hallmarks of compromise and messiness, was a huge hit and made Purcell's name on the London stage instantly. Ironically, Purcell's dramatic instincts had to find an outlet in incidental rather than integral 'operatic' music (plays with lots of spectacle was what the public wanted, with music an adornment of that spectacle), though Purcell would have been flattered that this was the first time a semi-opera had been entrusted to a single composer. So proud was he that he published the complete score. The constraints of semi-opera – where music and narrative are such uneasy bed-fellows – do give Purcell a free hand in some respects. If Dioclesian is the least stageable of the composer's four works in this genre, he evidently saw opportunities of characterization and mood-setting on a scale he had previously only dreamed and the Masque in Act 5, in particular, is a remarkably fine achievement of self-contained structural planning.
The success of any performance depends largely on conveying Purcell's fresh sense of adventure. This is something which all three versions detailed above achieve in their own way. Trevor Pinnock's new account is undoubtedly the one which reflects most strikingly the sense of gravitas and noble grandeur which constitutes much of the music in Acts 1-3. Stephen Gadd sings a magisterial ''Great Diocles'' and Pinnock's homogeneous and legato forces bathe luxuriously in Purcell's delectable counterpoint in the choruses. There is a sort of nonchalant virtuosity too about The English Concert (for example the Act 2 ritornellos) which one notices in the splendid Act 2 Symphony, but it loses its head in some of the wind playing (what are the trumpets up to in the Fourth Act Tune?).
Pinnock's closest competition comes from Richard Hickox, whose masques from Act 5 of Dioclesian were originally released separately from Acts 1-4, though the work – coupled with Timon – can now be bought complete. He offers a rather racier, more fleet-footed account which, if not representing the august sentiments of the play as strongly as Pinnock, breathes a delicacy and luminosity which I find more compelling over the long term, and Hickox revels in the choreographic implications of the instrumental dances. He can also boast a line-up of singers which is hard to beat; Catherine Pierard's ''Charon the peaceful Shade'' has a mellow, funereal poignancy which is better suited in this context than Nancy Argenta's brighter delivery, and not even Ann Monoyios can muster John Mark Ainsley's amorous longing in the famous song ''What shall I do?''. Much will depend on whether you prefer a soprano or tenor here. There is, however, a lot to admire in Pinnock: the masque is rather more adhesive than Hickox's (Timon is especially accomplished) and certainly he challenges Gardiner for poise. Paul Agnew sings wonderfully in ''Since the toils'', refined and shaped in a most musically unassuming way and ''Let the priests'', at the end of that number, has a marble-like gleam of great suavity. We are undoubtedly spoilt for choice but despite Pinnock's imposing view of this score, and Timon, Hickox is more malleable and reveals the hidden ironies which bubble beneath Purcell's surface finery.'