On their march to heavy metal immortality, Iron Maiden have left behind a wealth of buried gems. The punk- and New Wave of British Heavy Metal-inspired “Prowler” captures the Brits' raw side, while the 18-minute “Empire of the Clouds”, which showcases Bruce Dickinson on ivories, is Maiden at their most ornate. Yet another keeper is “Flash of the Blade”, a creepy slasher tale.