The day after his arrival, Fairfax attacked and defeated the royalists commanded by Biron, and took Colonel Monk prisoner.

He was sent to the Tower, where he endured, above two years, all the rigors of poverty and confinement.

The king, however, was so mindful as to send him, notwithstanding his own difficulties, a present of one hundred guineas; but it was not till after the royalists were totally subdued that he recovered his liberty.
Monk, however distressed, had always refused the most inviting offers from the parliament: but Cromwell, sensible of his merit, having solicited him to engage in the wars against the Irish, who were considered as rebels both by king and parliament, he was not unwilling to repair his broken fortunes by accepting a command which, he flattered himself, was reconcilable to the strictest principles of honor.

Having once engaged with the parliament, he was obliged to obey orders; and found himself necessitated to fight both against the marquis of Ormond in Ireland, and against the king himself in Scotland.

Upon the reduction of the latter kingdom, Monk was left with the supreme command; and by the equality and justice of his administration, he was able to give contentment to that restless people, now reduced to subjection by a nation whom they hated.