After getting the love potion (recipe) in No Rest for the Wicked, return to Pirkstein Castle and talk to young Lord Capon. Tell him you succeeded in your epic quest to find the Charlatan—eh, learned healer that is—and hand him the Musk of Infinite Allure.

(Location of Castle Pirkstein relative to the butcher)

He'll tell you his plan to recite love poems in the night to his beloved while he's under the guise of his newly acquired aphrodisiac. Only thing that's missing in his grande scheme is a wingman that can whisper the poems to him.

Seems like you don't really have a choice now do you? In any case, Lord Capon hands you the Anthology of Love Poems (good thing you've learned how to read) and tells you to go study it. I suggest that you do, because for the Wingman and True Friend achievements you will need to remember the poems correctly. Or rather, you need to memorize the first lines correctly.

So open up the anthology (or don't) and read the first poem. Remember, you only need to memorize the first lines correctly, and to make it even easier, it's only the first lines of the first three paragraphs in the anthology. They shouldn't prove too hard to remember:

Gentle night, why linger on?
I yearn thus for my love so long,
Without her words to still my breast,
Who shall set my soul to rest?

And now my heart in sorrow dwells,
From melancholic pining swells.
Since I, alas, was forced to part,
From the mistress of my heart.

Ah Lord, let me not wait in vain,
I yearn to see my love again!
Oh gentle Sir, be of good cheer,
I shall not cling to another dear.

Now regardless whether you read the anthology or not, head out for a stroll, play some dice, go get a girl at the bathhouse, or whatever tickles your fancy to pass the time. After a couple of hours, head back to Lord Capon. Enter his room at the third floor of Pirkstein Castle and... notice how it seems to be locked.

(Oh dearie! Hansie locked himself up in his room)

Well, it seems like the Musk of Infinite Allure did actually do something—in a way—because Lord Capon is covered in pimples. Be honest and tell him you don't look quite your best after that pass a speech check of 0 and reassure him that appearances aren't important — your words are! Well done chap! That did the trick, and Lord Capon is all ready to conquer the latest love of his life.

(Lord Capon gloating to his loyal henchman Heinrich)

Follow him into the dark starry night, where forlorn lovers linger under the gentle cloak of darkness in search of eternal love and happiness. Seems the young lord is quite overconfident of his abilities (must be the musk) and thinks someone will actually find his amorous adventures important enough to write about... yeah, whatever. Next he'll be telling us someone is going to create a DLC that centers specifically around his lordship...

Enter the churchyard of St. Matthew's Church and his lordship will tell you to hide behind some bushes or an obituary so that Karolina can't see you from her window. Well, turns out there is but one place you can hide—and it's neither a bush nor an obituary—namely, the small shelter next to her window.

(Shelter next to Karolina's window where you have to hide)

Do so and watch the cutscene. Remember the lines you were supposed to memorize? No? Good gracious! It's your time to shine and all replies are timed, what are you going to do? Scroll back in a hurry? Scream out? Wait! Alright, don't panic, here are the answers—again—for you:

• (First) Gentle night...
  
• (Second) And now my heart in sorrow dwells...
  
• (Third) Ah Lord, let me not wait in vain...

(Our starbound lovers in the performance of their life!)

That was quite the poem wasn't it? Lord Capon thinks so too, tell him to Blame it on the French!. Watch Capon disappear into the dark night, while you have to take care of his new paramour's father and henchmen.

(The butcher and his cronies)

You can either persuade (speech check 10), bluff (charisma check 14), or intimidate (strength check 15) miss Karolina's father. However, eventually you'll run out of witty things to say so start singing, and continue singing when prompted to and continue singing again when asked a third time.

Congratulations, you are a true messenger of love! At least if you did as you were told. The butcher and his henchmen should leave and you are left all alone in the cold night. This is also the moment where the Wingman badge should unlock!

Now, if you unlocked the Wingman achievement, then you will certainly also unlock True Friend. If somehow you were unable to keep the butcher and his cronies away, but you did recite the poem correctly, than you should also be able to get this. If you botched up the whole thing then you're out of luck and have to retry.

Regardless, head back from the churchyard to castle Pirkstein. Make sure to hold a torch (it's mandatory at night in Rattay) or risk a thrashing by the local guard. Wait till the next morning—8 am should do—and find Lord Capon still lying in bed.

(Lord Capon—seemingly cured from the Musk's pimples—congratulates Heinrich on a job well done)

Talk to him and ask him how the rendezvous went. Seems like he is quite ecstatic with himself and he congratulates his henchman—you, the messenger of love—with a deed well done! He'll also give you the love note he sent to miss Karolina, so you can learn from the best. Such gratitude! Exit the dialogue and the achievement is yours!

Q: I'm illiterate can you post the poems here?
A: Sure thing, here you are!

Gentle Night
I yearn thus for my love so long,
Without her words to still my breast,
Who shall set my soul to rest?

And now my heart in sorrow dwells,
From melancholic pining swells.
Since I, alas, was forced to part,
From the mistress of my heart.

Ah Lord, let me not wait in vain,
I yearn to see my love again!
Oh gentle Sir, be of good cheer,
I shall not cling to another dear.

To Love and Be Forlorn
To love and be forlorn
Is like night without a dawn.
To be close with nought to say,
Like winter frost in May.

To have lips and yet kiss not,
Is like leaving grain to rot,
To love without consumating
Is like unsown fields in the spring.

I shall love you then, my dear
As long as you lie with me here.
If you'll not give your all to me,
No longer shall I bide with thee.

Ode to Woman
Woman is the root of sin,
And yet of virtuous deeds again.
In Eden it was woman's deed,
To pluck the apple from the tree.

If you've no wealth to offer, you say,
She will scorn you and turn away,
But once you promise her treasure,
She says she will love you forever.

To murderous wrath she gives birth,
Leaving no peace on this earth.
Wounds inflicted by swords,
Cut less deep than women's barbed words.

Q: I can't find Capon's love letter, but I want to learn from the best! Can you post it?
A: Sure thing, here you are!

Capon's love letter
My sweetest, I am your most devoted secret admirer. Secret, for until I know you long for me as I do for you, I shall not make myself known to you. But once we know each other, then, my beloved poppet, I shall caress your t-ts and then I shall seek out the treasure you have carried with you since birth, for there is no lovelier creature than you. I only have to think of you and I raise a battle tent, the likes of which even Sigismund would envy! You must be mine and none other's! I shall take you to Paradise and back. You shall meet all the angels in heaven and call out to God more loudly than ever before! If you want to feel like no woman has ever felt before, put on this necklace tomorrow and I shall know that I should come to you in the night and slip inside your secret garden.

Your most ardent Secret Admirer

Q: Does anybody actually really ask these questions?
A: No actually they don't, I just make them up on the fly.

Q: Couldn't you just write a The Amorous Adventures of Bold Sir Hans Capon DLC walkthrough, instead of publishing these seperate guides? I mean, you've already covered 70% of the DLC...
A: I suppose I could, but I don't.

Q: But wouldn't it be much easier to just create one guide to rule them all?
A: Alright, you got me there. Truth be told, I started writing this guide a long time after I completed the Game of Throws quest... Which means I'd have to revisit an old save file, but right now it'd rather complete the game.

Q: Help! Some pictures aren't showing up!
A: Yeah, I know. Sometimes Steam Guides seems to randomly wipe uploaded images out from existence. The only thing that seems to work is reuploading the pictures, so just give a holler if the problem persists.

Q: I like this guide, did you happen to write some other KCD guides?
A: Much obliged! Yes, actually I also wrote a guide on the Friends-without-Benefits achievement (here), and the (Not-so-)Christian Burial and Ledetchko Revenant achievements (which you can find here). I also wrote a Achievement Guide and Walkthrough on the Band of Bastards DLC and the comprehensive Kingdom Come: Deliverance 100% Achievement Reference Guide.