Sir Thomas Fairfax saw Derby's absence as an opportunity to strengthen the Long Parliament's position in Lancashire and set out to conquer Lathom House.

Immediately after the fall of Warrington, the Parliamentarians requested that the countess acknowledge Parliament's authority and surrender her house, but she refused on the grounds that doing so would dishonour her husband.

The fortifications of Lathom House consisted of: In addition, the castle was at the lowest point in the middle of an open expanse that allowed superb views of the enemy's activities.

The uncommon situation of it may be compared to the palm of a man's hand, flat in the middle, and covered with rising ground around it, and so near to it, that the enemy in a two year's siege, were never able to raise a battery against it so as to make a breach in the wall practicable to enter the house by way of storm.

As a result, Parliamentary forces were unable to establish any major artillery positions against the castle, and the army refused to replenish those guns that were lost or spiked during the sorties.

One of the chaplains invoked the following verse from Jeremiah 50:14: Put yourselves in array against Babylon on every side: all ye that bend the bow, shoot at her, spare no arrows: for she hath sinned against the Lord.

She threatened to hang him from the tower gates, then asked him to convey the following while she tore the message: Carry this answer back to Rigby, and tell that insolent rebel, he shall have neither persons, goods, nor house.

When our strength and provisions are spent, we shall find a fire more merciful than Rigby; and then, if the providence of God prevent it not, my goods and house shall burn in his sight; and myself, children, and soldiers, rather than fall into his hands will seal our religion and loyalty in the same flames.

[citation needed]A similar ultimatum issued by Rigby on 23 May prompted Charlotte to respond: "The mercies of the wicked are cruel .... unless they treated with her lord, they should never take her or any of her friends alive".