King Henry V is betrayed in Act 2 Scene 2 by Lords Cambridge, Scrope and Grey, apparently without motive, though in fact, historically, they thought Henry V was not the rightful heir to the throne.
Shakespeare always likes to divest his evil characters of any real justification for their betrayal of others, particularly of those who have been gracious to them. Instead, he likes to attribute their "fall" to the temptation of "fiends", possibly in reflection of the betrayal of Judas whom Satan "entered". Imaginatively, he speculates here on whether there are "elite" devils in Tartarus (Hell), able to brilliantly tempt otherwise clever people to their own destruction:
"....Whatever cunning fiend it was
That wrought upon thee so preposterously
Hath got the voice in hell for excellence:
All other devils that suggest by treasons
Do botch and bungle up damnation
With patches, colours and with forms
Being fetch'd from glistering semblances of piety:
But he that temper'd thee bade thee stand up,
Gave thee no instance why though should'st do treason,
Unless to dub thee with the name of traitor.
If that same demon that hath gull'd thee thus
Should with his lion gait walk the whole world
He might return to vasty Tartar back,
And tell the legions "I can win
A soul so easy as that Englishman's".
Henry V Act 11, Scene 11
Shakespeare states that pure evil does not look for "pious" motives: it can easily enter someone, partly due to diabolical intelligence (if also through man's weak susceptible nature and lack of prayer). Evil can enter the soul of noble Englishmen. They too are prey for the hungry lion "that walks the world" and returns to vast(y) "Tartarus" (Hell) which is big enough for a mass of lost souls. This devouring lion is not "Aslan", the Lion of Judah (Jesus). This lion is the "prowling" lion, an image of the Devil from 1 Peter 5.8. Shakespeare conflates this lion with the nasty Satan of Job, who says to God that he has been "roaming through the earth, going back and forth" (Job 1.7). Shakespeare's terrifying lion has the face of the Devil. An Italian had rightly said to me that Shakespeare had to be a reformation Christian since he is so keenly aware of sin and evil.
In this instance, the evil the Poet envisages is the destruction of good government with all its civic woes in the strife of the War of the Roses which indeed ensued, through other means. These traitors were beheaded or quartered - but only by a broken-hearted King.
The message is this: be on your guard.