The adjective cloak-and-dagger means involving, or characterised by, mystery, intrigue or espionage.
The words cloak and dagger became associated with melodramas in the early 19th century; for example, the following is from Bell’s Weekly Messenger (London) of 3rd February 1811:
On Thursday night a new Opera, called The Peasant Boy, was produced at this Theatre.
An Italian Duke (Holland) goes to the wars; his cousin (Raymond) becomes anxious for the title and estates; he attempts to woo the Duke’s niece, but is rejected. Disappointed in love, he resolves on murder: and as the Duke is about to return at that precise period, he determines to murder him. A rencontre ensues, in which, after receiving a slight wound, Alberti is rescued by the sudden appearance at Ludovico (Lovegrove), who pursues the assassin, and wounds him in the right hand. The assassin Montalvi flies, and in escape the pursuit, which is close upon him, drops his cloak, mask, and dagger, at the door of a peasant’s cottage. Julian, the peasant’s son (Miss Kelly) comes out, and in the act of examining the cloak, is seized by the Duke’s servants. He is thrown into prison, and at length brought to trial, when, at the moment of sentence, Ludovico appears, and Montalvi is convicted of the crime.
On 26th May of that year, The Examiner (London) used cloak in collocation with dagger in a figurative sense:
Mr. Drakard, the Proprietor of the Stamford News, […] was brought up for judgment […] for a piece of writing, which, in exciting the public attention, has been the means of rousing Parliament to a sense of what it owed the general feeling, and of enabling military authority to commute scourging for confinement. […] [The Judge] expressed his indignation that the defendant, because he had adduced an instance in which he had sided against the popular feeling, and several instances in which he had denounced the conduct of Bonaparte, should have thought himself entitled to any respect on this occasion. […] It becomes to us to conclude, therefore, that in the opinion of the Learned Judge […], if you praise the conduct of Bonaparte, honest men justly cry out against you: but if you do not, nay, if you take all possible pains to hold it up to execration, and studiously to separate his moral worth from his talents, it is no matter:—your Judge will not think a jot the better of your spirit and impartiality:—nay, further still, Sir Vicary Gibbs will insist that you do it as a blind, as a cheat for the unwary, a cloak for some dagger that you are carrying about you!
The current form is first recorded in in Barnaby Rudge: A Tale of the Riots of Eighty (London, 1841), by the English novelist Charles Dickens (1812-70):
His servant brought in a very small scrap of dirty paper, tightly sealed in two places, on the inside whereof was inscribed in pretty large text these words. “A friend. Desiring of a conference. Immediate. Private. Burn it when you’ve read it.”
“Where in the name of the Gunpowder Plot did you pick up this?” said his master.
It was given him by a person then waiting at the door, the man replied.
“With a cloak and dagger?” said Mr. Chester.
With nothing more threatening about him, it appeared, than a leather apron and a dirty face.
Reporting on his recent visit to Greece, cradle of the Western theatre, Kenneth Tynan, dramatic critic, punned on cloak-and-dagger in Journey to the cradle, published in The Observer (London) of 1st July 1962:
There were some 40 of us in all—playwrights, designers, architects, directors and critics, invited by the Greek Tourist Office to take part in a Unesco conference on “mass spectacles” and their place in the theatre of the future.
Except by a solitary Rumanian, the Iron Curtain countries were unrepresented in our debates: beneath the façade of international amity there lurked an unmistakable element of colloque-and-dagger.
It is possible that cloak and dagger is a variant of cloak and sword, which, like French de cape et d’épée, translates (comedia) de capa y espada, a Spanish literary term for a type of dramas of romance, intrigue and melodrama in which the main characters are from the ranks of society which formerly wore cloak and sword or dagger. One of the dramatists who established the popularity of this type of plays during the Spanish Golden Age (approximately from 1492 to 1659) was Lope de Vega Carpio (1562-1635).
English cloak and sword was introduced by Henry Richard Vassall-Fox (1773-1840), 3rd Baron Holland, in Some Account of the Life and Writings of Lope Felix de Vega Carpio (London, 1806):
The plays of that period do not admit of the distinction of tragedies and comedies, according to the common, or at least the French acceptation of those terms. They are not comedies; for not only distressing situations and personages of high rank, but assassinations and murders are admitted into their plots: on the other hand, the sprightliness of the dialogue, the lowness of some of the characters, the familiarity of the language, and the conclusion of the piece, which is generally fortunate, deprive them of all claims to the title of tragedies. Yet even in Lope’s works there is an evident difference in his conception as well as execution of two distinct species of dramatic compositions. In one, the characters and incidents are intended to excite surprise and admiration; in the other, merriment mixed occasionally with interest. Love indeed is the subject of both: but in one it is the love which distinguished the ages of chivalry; in the other, the gallantry which succeeded to it, and which the poets had only to copy from the times in which they lived. The plays of the latter description, when the distinction became more marked, acquired the name of Comedias de Capa y Espada, Comedies of the Cloak and Sword, from the dresses in which they were represented; and the former that of Heroic Comedies, from the character of the personages and incidents which compose them.
The English novelist Hugh Seymour Walpole (1884-1941) used the expression in The Young Enchanted: A Romantic Story (London, 1921):
In literature her great period had been during the Romantic Tushery¹ of 1895 to 1905. How she had torn and scarified the Kailyard novelists², how the Cloak and Sword Romances had bled beneath her whip. Now none of these remained, and the modern Realism had gone far beyond her most confident anticipations.
¹ tushery: used by the Scottish poet, novelist and travel writer Robert Louis Stevenson (1850-94) for a conventional style of romance characterised by excessive use of affected archaisms such as ‘tush!’; hence, sentimental or romanticising writing
² Kailyard School: a late-19th-century movement in Scottish fiction characterised by a sentimental idealisation of humble village life
According to a mistaken theory, cloak-and-dagger has its origin in fencing: the cloak, wrapped around one arm, was used as a defensive weapon. These illustration and quotation are from Old Sword-Play: The Systems of Fence in vogue during the XVIth, XVIIth, and XVIIIth centuries (London and New York, 1892) by Alfred Hutton (1839-1910):
Rapier and Cloak.
In this exercise the Cloak takes the place, as a defensive weapon, of the buckler or the dagger. It must be turned twice round the left arm in such a manner as to cover the elbow, while the collar is grasped in the left hand the ends are to be passed over the arm so as to hang down in folds on the outside of it, and with these folds (never with the part which rests on the arm) the various attacks are parried. (Plate 30-)