In act 1, scene 2 of Shakespeare's Hamlet, Polonius's son, Laertes, asks King Claudius for permission to return to France. Claudius grants Laertes's request, after consulting with Polonius:
KING. (To Laertes) Have you your father's leave? (To Polonius) What says Polonius?
POLONIUS. He hath, my lord, wrung from me my slow leave
By laboursome petition, and at last
Upon his will I seal'd my hard consent.
I do beseech you, give him leave to go. (1.2.59-63)
In act 1, scene 3, the ship taking Laertes back to France is ready to set sail. Polonius and Laertes's sister Ophelia are seeing Laertes off, but not before Polonius gives Laertes some fatherly advice, which includes the famous lines, "Neither a borrower nor a lender be," and "to thine own self be true" (1.3.79, 82)
By act 2, scene 1, Laertes is in France and living in Paris. In the scene, Polonius confers with his servant, Reynaldo, whom Polonius is sending to Paris to give money to Laertes, and "to make inquire / Of his behaviour" (2.1.45)—in other words, to spy on Laertes.
Polonius advises Reynaldo that the best way to get information about Laertes is by modest subterfuge and deception. Polonius tells Reynaldo to first find other Danes in Paris, engage them in small talk and polite conversation, and find out if they happen to know Laertes. At the same time, Reynaldo must not tell anyone how well he actually knows Laertes, but only that he has "some distant knowledge of him" (2.1.14)
If the person with whom Reynaldo is speaking knows Laertes, Reynaldo should say that he's heard stories about Laertes's behavior, "and there put on him / What forgeries you please" (2.1.20-21), and lead the person into telling what he knows about Laertes.
In other words, Reynaldo is to say that he's heard that Laertes has done such-and-so, and then see if that will get the other person to open up about Laertes, and either confirm or deny that particular kind of behavior:
REYNALDO. As gaming, my lord?
POLONIUS. Ay, or drinking, fencing, swearing, quarrelling,
Drabbing. You may go so far...but breathe his faults so quaintly
That they may seem the taints of liberty... (2.1.26-34)
Polonius then outlines for Reynaldo what the other person is likely to say:
POLONIUS. ‘I know the gentleman.
I saw him yesterday,’ or ‘t'other day,’
Or then, or then, with such, or such; ‘and, as you say,
There was a gaming,’ ‘there o'ertook in's rouse,’
‘There falling out at tennis’; or perchance,
‘I saw him enter such a house of sale,’
Videlicet, a brothel, or so forth. (2.1.62-68)
Polonius reasons that if Reynaldo tells little lies about Laertes to the other person, that person might be tricked into giving other information about Laertes's behavior that Reynaldo can report to Polonius:
POLONIUS. And thus do we of wisdom and of reach,
With windlasses and with assays of bias,
By indirections find directions out. (2.1.71-73)
Polonius is saying that by telling little lies ("indirections") about Laertes, Reynaldo can find out the truth about his behavior.
It should be clear to the audience by now that Polonius is a meddlesome and controlling character, but there seems to be another reason for sending Reynaldo to spy on Laertes.
Polonius clearly warns Reynaldo against saying anything that will discredit or dishonor Laertes.
POLONIUS. ... [P]ut on him
What forgeries you please—marry, none so rank
As may dishonour him, take heed of that... (2.1.20-23)
A little later in the scene, Polonius follows up the line about dishonoring Laertes with an intriguing reference:
POLONIUS. You must not put another scandal on him... (2.1.31)
Nothing more is said about the "scandal" in this scene or at any other time in the play, so the nature of the "scandal" remains a mystery.
However, there might be a subtle reference to Laertes's "scandal" in act 1, scene 3 that explains Polonius's rational for sending Reynaldo to spy on Laertes.
In act 1, scene 3, Laertes lectures Ophelia about her relationship with Hamlet, and cautions her against losing her honor, losing her heart, or leaving her "chaste treasure open / To his unmast'red importunity" (1.3.34-35).
Ophelia has a telling response to Laertes's brotherly advice which provides insight into Laertes's behavior when he's away in France, and which might also refer to Laertes's "scandal":
OPHELIA. I shall the effect of this good lesson keep
As watchman to my heart. But, good my brother,
Do not, as some ungracious pastors do,(50)
Show me the steep and thorny way to heaven,
Whilst, like a puff'd and reckless libertine,
Himself the primrose path of dalliance treads
And recks not his own rede. (1.3.48-54)