There Can Be Only One Secondary Quest, Blood and Wine Quest
Related points of interest
Stages of "There Can Be Only One" quest
1. Investigate the isle on Lac Célavy.
Upon a notice board in Toussaint, Geralt found a call to all who wished to submit to a Test of Virtue. The notice's mysterious author summoned any who dared to an isle upon Lac Célavy, where they would have a chance to prove their worthiness of character. He who successfully completed the test would receive a reward. Though Geralt had never thought of himself as particularly virtuous, he found the summons intriguing and decided to go to the appointed spot to learn what the trials entailed.
3. [Optional] Read the inscriptions on the stones.
On the lakeshore Geralt encountered a hermit who promised the witcher a wondrous blade. To receive it, Geralt had to prove he lived by the five chivalric virtues.
The inscriptions on these stones describe the five virtues - valor, honor, wisdom, sympathy and generosity.
4. Wait for a chance to prove you are capable of compassion.
Mercy is not something folk expect of witchers. As it is, they were created to hunt and kill monsters, and the mutations they undergo as children customarily strip them of all emotions. Yet Geralt had always been somewhat different, so when push came to shove he passed the Trial of Compassion, for he had always striven simply to be a decent man in spite of all.
5. Wait for a chance to prove your generosity.
Paradoxically, it is sometimes easier to demonstrate valor or honor than it is to show generosity. For the fact is many are courageous and honorable simply to advance their own cause. Geralt, like all witchers, worked for coin, but always knew well when a situation required him to show generosity. No surprise, then, that he successfully passed the trial meant to test this virtue.
6. Wait for a chance to prove your wisdom.
Among the virtues, wisdom is arguably hardest to prove, for many consider themselves wise, yet the world is full of fools. Geralt never thought of himself as excessively wise, and perhaps this is why he managed to prove this virtue was no stranger to him.
7. Wait for a chance to prove you are a man of honor.
At times it is hard to keep one's word and thus demonstrate honor when faced by temptation. Luckily, Geralt was stouthearted and successfully completed the Trial of Honor.
8. Wait for a chance to prove your valor.
Many consider themselves courageous, yet when confronting true danger prove consummate cowards. Naturally, this applies in no way to Geralt, who faced mortal danger and vanquished it post haste, thus successfully passing the Trial of Valor.
9. Tell the hermit you're ready to fight him.
The witcher met a hermit threw down the gauntlet, brazenly challenging Geralt to a duel.
11. Quest completed.
After a fierce and beautiful fight, Geralt defeated the hermit. The witcher was then greatly surprised to learn the man was in fact the Lady of the Lake in disguise, a woman Geralt had encountered long past on his Path. As the hermit had promised, the Lady bestowed upon Geralt the legendary sword called Aerondight.