The Two Towers by J.R.R Tolkien (Harper Collins 1991, 2007) pp.646-650
The treason of Isengard is one of the saddest stories within all that makes up The Lord of the Rings. One who was chosen by the Valar to rouse the peoples of Middle-earth against Sauron chooses to turn against them and to side with the very power against whom he was sent to fight.
Gandalf has been giving Aragorn, Legolas and Gimli a briefing on the state of affairs in the War of the Ring at this point in the story when he has been reunited with them in Fangorn Forest. He has spoken of how Sauron has no conception of the possibility that his enemies might want to destroy the Ring, being convinced that one of them will seize control of it and use it against him. With this conviction he is concentrating upon attack rather than defence. “If he had used all his power to guard Mordor, so that none could enter, and bent all his guile to the hunting of the Ring, then indeed hope would have faded: neither Ring nor bearer could long have eluded him.”
But what Sauron believes is that it will take time even for the most able of his enemies to learn how to wield the power of the Ring in a way that could ensure victory over him. Gollum, and then Bilbo later, possessed and used the Ring, but neither were able to do much more with it than to make themselves invisible. As Frodo draws nearer to Mordor he begins to become more aware of the Ring’s power threatening to use that power against Gollum in order to frighten him into co-operation, but compared to what Sauron could achieve if he were to regain possession of the Ring this is very small.
Because of this Sauron believes that he has a window of opportunity to strike a blow against his foes that will be strong enough to defeat them. His main goal is to capture Minas Tirith, the capital of Gondor and that is where the main part of his attention is focussed. Surely this is the reason why he sent only a small company of orcs to waylay the Fellowship and not a more significant force. His concern would have been that any larger company would have attracted the attention of his enemies and he did not yet have enough control over the territory between Mordor and the Anduin to fight a battle far from home.
So Grishnákh’s force that took part in the attack upon the Fellowship was not particularly large, and disastrously for Sauron, not large enough to force Uglúk’s Uruk-hai to go to Barad-dûr instead of Isengard.
“Already he knows that the messengers that he sent to waylay the Company have failed again. They have not found the Ring. Neither have they brought away any hobbits as hostages. Had they done even so much as that, it would have been a heavy blow to us, and it might have been fatal. But let us not darken our hearts by imagining the trial of their gentle loyalty in the Dark Tower. For the Enemy has failed- so far. Thanks to Saruman.”

Gimli is confused by Gandalf’s words, wondering if what he means by them is that Saruman is not a traitor, but what Gandalf means is that Saruman is not only a traitor to the Valar and the free peoples of Middle-earth but also to Sauron. Saruman wants the Ring for his own purposes. He wishes to become lord of Middle-earth. But he too has failed to seize the Ring. He too has not even been able to capture hobbits. All that he has managed to achieve is, as Gandalf puts it, “to bring Merry and Pippin with marvellous speed, and in the nick of time, to Fangorn, where otherwise they would never come at all.”

What Saruman has achieved by attempting to seize the Ring for himself is to make Sauron aware of his treachery. At this point of the story Sauron fears that it might be Saruman who has seized the Ring. Time and again irony has a big part to play within The Lord of the Rings. An action that is meant to do harm turns out to achieve the opposite of its intention. It might even be that irony is not merely a kind of chance event but is woven into the very fabric of reality.