The Súgan Earl's large army, which numbered up to 3,000 men had shadowed Carew's force on their progress to Glin and watched them closely upon their preparation of the siege but did not intervene due to disunity in their ranks.

On the 7th of July, the Knight met with his relative, the Earl of Thomond who attempted to persuade him to order the castle's surrender, being shown the array of cannons and informed that Carew intended to execute his young son whom he held hostage.

A list of the commanders of this Third Desmond uprising was immediately provided to the English authorities by an informant by the name of Owen Moriarty.

Carew had previously written to the privy council claiming the Knights of Glin and Kerry had importuned to be received into queen's favour and if they did not continue on this path it was due to the influence of Florence McCarthy.

He was a master of intrigue, and offered Dermot O'Connor, the mercenaries of Connacht's leader, £1,000 and other favors in exchange for the Sugan earl's delivery.

The behaviour of the earl and his supporters during the siege and conquest of Glin castle in July 1600 made clear this, the absence of a larger strategy, and their lack of cohesion.

Carew and his soldiers travelled 20 miles via Ballintore on Sliabh Luachra, passing while being watched by the forces of the Sugan earl, whose camp was close to Athea.

The soldiers of Glin Castle demolished a number of thatched homes nearby in what was known as Mill Street as Carew drew closer.

The Sugan earl and his supporters had set up on a position around Ballyguiltenane on the hills overlooking the castle when Carew arrived at Glin at noon on July 5.

Carew disregarded them and proceeded to set up a siege on Glin castle, most likely because he was aware of the severe division among the forces of the Sugan earl.

There they found Gawen Harvey at anchor (he had fought off the rebels for the previous two weeks and had killed two) before the Castle (on the Shannon Estuary) with their ordnance.

On the 7th, Edmund fitz Thomas, the knight of Glin, who had been seeing the action from a vantage point at a location known as Tullyglass, dispatched a messenger to Carew's camp requesting for a safe journey.

Edmund again conferred with Thomond but was again resisted Carew's ultimatum to give the castle's capitulation orders and left the camp to watch the progress of the siege from his vantage point.

After this was granted, he spoke to the Earl, representing to be his 'natural follower' (the constable was Thomond born) and wishing to, in his best interests warn him of the peril he would be in if he joined the siege as "the earl of Desmond and the Connachtmen ... 3,000 strong at least" were "not two miles from this place ..." and would attack Carew's camp upon the commencement of the siege whereupon they would be put to the sword and driven into the River Shannon.

Early the next morning, on 8 July, the gunner found the touch-hole clogged on the demi-cannon, which was timed to commence the attack on the castle with a bombardment.

The eighty-man garrison was split into two sections, one of which was commanded by Donall na Searrach (Daniel of the colts) Culhane, a member of a family who were hereditary constables of Glin castle, and the other by Tadhg Dore.

Later, in a letter to Hugh O'Neill, Edmund claimed that the division was the result of "the sinister dealings of Connacht men," most likely alluding to Dermot O'Connor's actions, who, following his initial betrayal, later rejoined the earl of Desmond's forces.

Captain Flower (thought to be the ancestor of Robin Flower), also referred to in folklore as "An Captaen Riabhach" (the "swarthy captain"), and a chosen group of men entered through the breach and fought their way from a vault into the great hall, forcing the warders into a castle close adjoining it where from out of a spike they killed four soldiers (possibly done by the three Giltenan brothers whom Culhane mentions).

A second assault was led by Turlough Roe MacMahon (father of Maire Ruadh McMahon), of Colmanstown Castle, County Clare.

The constable was killed in a short engagement (his head was then put on a stake), and with the exception of two who managed to escape, the garrison was driven back inside the castle.

Carew spent five days getting the castle at Glin rebuilt and garrisoned it with 20 soldiers under Captain Nicholas Mordant because he believed it to be of significant strategic value.

He was referred to as "An Famaire Riabhach" (literally, "the swarthy monster"), and ever since, the Glin neighborhood has used his memories to frighten mischievous kids.

[3] Carew, recognizing the chastening effect the siege had on the rebels, reported to the privy council on August 25 that "(John) O'Connor) did never send or come into me until the Glan was taken, and two cannon in a boat ready to sail to his castle of Carrigafoyle."

He went south to fight at Kinsale where he was wounded and saved from death by one of his follower's Donough Costelloe, a member of the family which fostered the children of the knights of Glin.

After this a general pardon was given by the English to those who had taken part in the rebellion, but Edmond was excluded by name (along with Donal O’Sullivan Beare, Thomas Fitzmaurice of Lixnaw, John O’Connor of Carrigafoyle, Oliver Hussey and others).