In 1769, the poet Thomas Chatterton, only 17 years old, sent Horace Walpole the first of a series of poems supposedly written by a 15th-century monk named Thomas Rowley but really written by Chatterton himself.
Other poems followed, and Walpole was briefly taken in but later reconsidered.
When Chatterton committed suicide the following year, there were rumours that Walpole's treatment of the young man had played a part.
Despite Walpole's scepticism, in 1777, shortly after Edmond Malone's arrival in London, Thomas Tyrwhitt published Chatterton's forgeries as Poems, Supposed to Have Been Written at Bristol, by Thomas Rowley and Others, in the Fifteenth Century.
This created a great controversy, with much debate about their authenticity.
For the third edition in 1778 he added an appendix arguing against the poems' antiquity, and Thomas Warton, in his The History of English Poetry (1778), devoted an entire chapter to it.
Those favouring the authenticity of the Rowley poems responded in late 1781 when, just days apart, Jacob Bryant, a classical scholar, published Observations upon the Poems of Thomas Rowley; in Which the Authenticity of Those Poems is Ascertained, and Jeremiah Milles, Dean of Exeter and President of the Society of Antiquaries of London, published Poems, Supposed to Have Been Written at Bristol, in the Fifteenth Century, by Thomas Rowley, Priest, &c.; With a Commentary in Which the Antiquity of Them Is Considered and Defended.

The controversy was a perfect match for Malone: steeped in ancient and early modern English literature, by trade a lawyer, and with no patience for literary forgeries or those who entertained them.
As Martin puts it he "entered the fray" in December 1781 by "[sending] an anonymous 'brat into the world'" The "brat" was an article in two parts in The Gentleman's Magazine, signed "Misopiclerus".
The essay met with success, and by February he published a second edition as Cursory Observations on the Poems Attributed to Thomas Rowley.
In the essay he compares the Rowley poems to poetry by actual writers of the era; shows Chatterton's sources to have been later writers like Shakespeare, Pope, and Dryden; picks holes in the arguments put forward by Chatterton's supporters; and ends on an awkward attempt to ridicule Bryant and Milles.

I do humbly recommend, that … the friends of the reverend antiquarian … and the learned mythologist … may, as soon as possible, convey the said [gentlemen] to the room over the north porch of Redcliffe church, … that in order to wean these gentlemen by degrees from the delusion under which they labour, and to furnish them with some amusement, they may be supplied with proper instruments to measure the length, breadth, and depth, of the empty chests now in the said room, and thereby to ascertain how many thousand diminutive pieces of parchment, all eight inches and a half by four and a half, might have been contained in those chests; (according to my calculation, 1,464,578;—but I cannot pretend to be exact:).

— Edmond Malone, Cursory Observations on the Poems Attributed to Thomas Rowley
In 1769, the poet Thomas Chatterton, only 17 years old, sent Horace Walpole the first of a series of poems supposedly written by a 15th-century monk named Thomas Rowley but really written by Chatterton himself. Other poems followed, and Walpole was briefly taken in but later reconsidered. When Chatterton committed suicide the following year, there were rumours that Walpole's treatment of the young man had played a part. Despite Walpole's scepticism, in 1777, shortly after Edmond Malone's arrival in London, Thomas Tyrwhitt published Chatterton's forgeries as Poems, Supposed to Have Been Written at Bristol, by Thomas Rowley and Others, in the Fifteenth Century. This created a great controversy, with much debate about their authenticity. For the third edition in 1778 he added an appendix arguing against the poems' antiquity, and Thomas Warton, in his The History of English Poetry (1778), devoted an entire chapter to it. Those favouring the authenticity of the Rowley poems responded in late 1781 when, just days apart, Jacob Bryant, a classical scholar, published Observations upon the Poems of Thomas Rowley; in Which the Authenticity of Those Poems is Ascertained, and Jeremiah Milles, Dean of Exeter and President of the Society of Antiquaries of London, published Poems, Supposed to Have Been Written at Bristol, in the Fifteenth Century, by Thomas Rowley, Priest, &c.; With a Commentary in Which the Antiquity of Them Is Considered and Defended.
The controversy was a perfect match for Malone: steeped in ancient and early modern English literature, by trade a lawyer, and with no patience for literary forgeries or those who entertained them. As Martin puts it he "entered the fray" in December 1781 by "[sending] an anonymous 'brat into the world'" The "brat" was an article in two parts in The Gentleman's Magazine, signed "Misopiclerus". The essay met with success, and by February he published a second edition as Cursory Observations on the Poems Attributed to Thomas Rowley. In the essay he compares the Rowley poems to poetry by actual writers of the era; shows Chatterton's sources to have been later writers like Shakespeare, Pope, and Dryden; picks holes in the arguments put forward by Chatterton's supporters; and ends on an awkward attempt to ridicule Bryant and Milles.
I do humbly recommend, that … the friends of the reverend antiquarian … and the learned mythologist … may, as soon as possible, convey the said [gentlemen] to the room over the north porch of Redcliffe church, … that in order to wean these gentlemen by degrees from the delusion under which they labour, and to furnish them with some amusement, they may be supplied with proper instruments to measure the length, breadth, and depth, of the empty chests now in the said room, and thereby to ascertain how many thousand diminutive pieces of parchment, all eight inches and a half by four and a half, might have been contained in those chests; (according to my calculation, 1,464,578;—but I cannot pretend to be exact:).
— Edmond Malone, Cursory Observations on the Poems Attributed to Thomas Rowley
Edmond Malone