In the play Macbeth, deception plays
a vital part in the development of characters
and the plot. Discuss.

In Shakespeare's Macbeth a striking theme of betrayal and decption is created almost immediately, and this theme is dominant throughout the development of characters and the development of the plot as a whole. 
The deception in the play can be subcategorised: the direct agents of deception; the influenced agents of deception; the victims of deception and betrayal.
Immediately, the opening scene creates a sense of disorder by the appearance of the witches and this disorder is directly emphasised by the Thane of Cawdor's betrayal to the throne. This introduces the theme and also makes the audiance aware that if the order of the throne is challeneged, death results, sealing Macbeths fate, in only the second scene.
This scene also introduces Macbeth as 'noble Macbeth' which I believe is to contrast his courageous spirit with his malicious act.
In the scene which follows we are introduced, visually, by Macbeth and Banquo as they are confronted by the Witches, who proclaim:

'All hail Thane of Glamis,
All hail Thane of Cawdor
Macbeth shall be king hereafter'

Immediately, Macbeth is informed of his promotion from Thane of Glamis to Thane of Cawdor. Banquo is aware of the evil of the witches;

'Could the devil speak true?'

But Macbth is intriqued by the prophecy and reveals prior thoughts of murder and betrayal:

'My thought of murder is yet but fantastical'

This begins the deception of Macbeth's mind, one which is inevitably destined for failure.
When Macbeth informs Lady Macbeth of the prophecies, her first words express her fear of Macbeth's abilities and confirm the plan to murder Duncan;

'I fear he is too full o' the milk of human kindness.'

It could be argued that Lady Macbeth betrays Macbeth, aware of his noble spirit, she exploits him, challanges him, doubts him.
With this in mind, it is important to remember that Lady Macbeth and Macbeth required furthur assistance in order to complete the deed, displaying their initial conscience, which will be their downfall in the end. Lady Macbeth calls for evil spirits to:

'Unsex me here and fill me from the crown to the toe
with the direst cruelty.'

In Elizabethen times, this would have immediately condemed Lady Macbeth, though she is not completely guilt ridden;

'I would hath done't had he not resembled my 
father as he slept'

Of course, it can be argued that Lady Macbeth was somewhat deceptive towards Macbeth, encouraging him to do what he found challenging, morally and consciously. Yet, the question remains, would Macbeth have killed Duncan without Lady Macbeth? Based on this statement, I believe Lady Macbeth was deceptive towards Macbeth, at least to an extent.
The theme of deception is furthur emphasised when Duncan is murdered and 'mousing owls kill hawks', horses eat each other and night becomes day. The rightful hier has been removed and God's order will not return until the rightful heir is restored.
Although betrayal is a common theme, Banquo rejects these tendencies and stays loyal to Macbeth, even though he suspects him of the murder of Duncan. I believe this is effective in highlighting Macbeth's sheer ruthlessness in murdering the loyal Banquo and attempting to murder his son, Fleance. Still, both he and Lady Macbeth are not free of remorse:
'Act the innocent flower, but be the serpent under it'
'A false face hides what a false face doth know'

The 'false face' Macbeth displays, furthur exposes the theme of deception. The betrayal involved in the murder of Banquo is, I believe stronger than the betrayal against Duncan. It can be argued that Duncan was a king and Banquo but a soldier, but Banquo was also a loyal friend to Macbeth and the appearance of Banquo's ghost at the banquet scene furthur seconds this idea.
As the play progresses, betrayal becomes less of an issue, although it can be argued Macbeth was betrayed. The theme of deception dominates the play as the end approaches. Macbeth seeks out the witches in order to put his mind at rest. The fact that Macbeth seeks the witches help displays his complete transfer to evil and even the witches call him 'something wicked'.
He is lead into a false sense of security by the witches and he is shown three apparitions, each find him confident. Is Macbeth more eager to accept what he is told, at such a vulnerable stage? And when told 'no man of woman born shall harm Macbeth', he exclaims the impossibility of this. Are the witches decpeting him on purpose?
In this play, betrayal and deception are central themes and play a vital role on an audiences view of a character, one which Shakespeare not only exploits magnificently but suceeds in watching the development of a character, may it be from noble to the depths of evil.