After Di Renjie broke "The Case of the Rain Master", because of the order of the Empress Wu, he was transferred to Lanfang County, deep in the desert, and he had to face the situation of the Lanfang Mountains left behind after the black flame control, and how he broke the situation became the key. 
The Case of the Rain Master is illogical to solve the case "The Case of the Rain Master" started by Boss Zhong, who fell in love with Huang Ying'er, and did not hesitate to go bankrupt for her, no longer taking care of the pawnshop, and pretending to be a rain master, but his actions caused the dissatisfaction of the shopkeeper Lin who had followed him for more than 20 years, and the shopkeeper Lin killed Boss Zhong because of jealousy, and gave him a fatal blow from behind, as for the knife in front of Boss Zhong's corpse, it was actually given by Huang Ying'er, Huang Ying'er saw Boss Zhong's face, and knew that he had been deceived, So stabbed him with a dagger. 
The rain division disappeared since then, Di Renjie had no clue at first, and even suspected that it was done by four teenage soldiers, but later the barracks ordnance embezzlement case was revealed, and Di Renjie found out the truth and confirmed that it was not these four soldiers who killed Boss Zhong, so who is **? In the end, Di Renjie found the shopkeeper Lin, and the funny thing is that he asked the other people in the pawnshop to know the origin of the pawn ticket and the pawn. 
But even if Di Renjie knew that ** was indeed the shopkeeper Lin, there was no evidence in his hands at all, why did the shopkeeper Lin pretend to be stupid, but finally admitted that he killed Boss Zhong? Obviously, this is a very unreasonable thing to do. What's even more unreasonable is how did Di Renjie convict Shopkeeper Lin? You must know that he simply does not have enough evidence to prove that Shopkeeper Lin killed Boss Zhong. 
And Shopkeeper Lin said that he killed him in front of him, what can he do? Di Renjie can't be convicted at all, as long as Shopkeeper Lin bites himself to death and doesn't kill anyone, relying on a pawn ticket, he can't be convicted of his crime at all. But the strange thing is that in the end, Di Renjie still arrested the shopkeeper Lin, it can only be said that it is really too strange, and the whole case is illogical and embarrassing. 
It's not just the Yushi case, in fact, the previous cases give people the feeling that they are unreasonable, and they don't rely on evidence to catch **, and the final outcome is also unsatisfactory, and they are not punished by the law, but Di Renjie decided with a word, and then** went offline inexplicably, such as Wei Wuji, and Hou Yu. 
The most dangerous enemy hid beside Di Renjie With Di Renjie being transferred to Lanfang by the order of the Empress Wu, Di Renjie was originally very entangled, but in the end he showed his mind to Cao An, Cao An was still angry and even hard-mouthed, but in the end he followed Di Renjie to Lanfang and let go of everything in Penglai County, although this is very strange, but it is also understandable, it is reasonable to say that she is brave for love. 
But one thing happened later but people think about it and feel very wrong, on the way to Lanfang, Di Renjie encountered a sandstorm, everyone naturally avoided the sandstorm, but the case file brought by Di Renjie was blown down by the sandstorm, Di Renjie went to find his case file but touched a peach wood sword, and the peach wood sword was the peach wood sword he loved when he was a child, Di Renjie lost it, and his heart was very excited. 
But the question is who put this peachwood sword in that position? Obviously, this peachwood sword could never happen to appear in **, but someone in the whole team knew the effect of this thing on Di Renjie, so where did it be placed on purpose, so who is this person? Regarding this question, the answer is actually obvious, Ma Rong and Qiao Tai are unlikely, Hong Liang is Di Renjie's person, if he has it, he can be handed over to Di Renjie, there is no need to bother, the only possibility is Cao An.
If you take a closer look at some of the previous cases, you will find that Cao An has actually appeared in every case, and it is no exaggeration to say that Cao An has always been by Di Renjie's side, and even the first case "Fengyin Case" has her figure. Di Renjie once saw her true face through the lake, and he heard the Bingzhou minor tune near the theater that the Empress Wu once praised, and this Bingzhou minor tune was most likely sung by Cao An.
One is because when Cao An saw Hei Yan for the second time in his memory, Hei Yan asked her if she would sing Bingzhou Minor, and she said no, and her attitude towards Hei Yan showed that it was very likely that she would learn Bingzhou Minor: for him. The second is that the old bustard in the theater where she is located once replied to Di Renjie that Cao An is practicing the state minor, which is enough to confirm that Cao An can sing the state minor.
From here, it is not difficult to know that Cao An's true identity is not simple, and even she is the most dangerous enemy, because the mysterious unknown is the real danger. Cao An even suggested Di Renjie in the new plot, saying that the case of Hongtingzi will be Di Renjie's game-breaking case in Lanfang, it can be seen that her control of the situation is indeed very powerful, if she has evil intentions, Di Renjie will definitely die.
In short, judging from these analyses, Cao An is definitely the most dangerous existence around Di Renjie, she definitely appeared by Di Renjie's side with a purpose, and her position is unclear, she is the most dangerous enemy, she has always been hidden by Di Renjie's side and ignored.
Cao An is Black Flame's person? Cao An must have a purpose hidden by Di Renjie's side, whose person is Cao An has become the key to this question, in fact, who is Cao An's person, it is not difficult to analyze, there are three possibilities: one is that she is the person of the Empress Wu, second, she is the person of Black Flame, and third, she is close to Di Renjie with a purpose, not anyone's person. It is clear that all three possibilities exist.
We know that Cao An's father is called Cao Hexian, in the original book, in fact, Cao An's father Cao Hexian participated in the ** case, and Cao An was very miserable in the original book, and was tarnished several times, but in the drama version of her father because he participated in the private copper coin case, so his house was raided, Cao An's life experience is very special, so who is she? Let's analyze three possibilities.
First of all, the reason why she is said to be the person of the Empress Wu is very simple, because the reason why Di Renjie was involved in the power struggle in the Fengyin case was because Di Renjie and He Dajing entered a trick hall, and in the end He Dajing died. The reason why Di Renjie entered that theater was because he heard a minor tune of the state and state, who sang this minor tune? There is a high probability that it is Cao An, deliberately attracting Di Renjie into it.
Although Cao An said that she would not be able to merge with the state minor, but in fact she would, when she was in Penglai County, Di Renjie asked the bustard, and the bustard said that Cao An was practicing, and when Heiyan saw her for the second time, he asked her if she would, she would not at the time, but later she learned to merge with the state minor tune, and Cao An indirectly helped the Empress Wu to complete the plan and lead Di Renjie into the game, it is likely that she is the person of the Empress Wu.
As for the second possibility that she is Black Flame's person, it is also easy to explain, she was rescued by Black Flame when she was a child, and later Black Flame took her to many places with her, went to the desert, and even Lanfang may have been there when she was a child. Therefore, Cao An likes Black Flame, becomes his person, and helps him monitor Di Renjie, this possibility is also very large.
As for the third possibility, if Cao An is just the daughter of a criminal minister, and approached Di Renjie in order to wash away her father's grievances, then she should tell Di Renjie the truth early, there is no need to follow like this all the time. Among these three possibilities, in fact, the most likely is the second one, for three reasons, one is that Black Flame saw Cao An on the ship at the time of the ** case, and the two obviously recognized each other and made eye contact. Second, Di Renjie encountered a sandstorm in the desert, and when he was looking for the file, he found the peachwood sword, which could only be secretly buried by Cao An, and Black Flame was most likely Di Renjie's brother-in-law, so he gave it to Cao An, and Cao An gave this peachwood sword to Di Renjie with such presumptuousness, and the third is naturally that Cao An and Black Flame have a very close relationship.
All in all, Cao An is most likely a person from Black Flame, and he has been staying by Di Renjie's side for other purposes, either to protect, or to monitor, or to give Di Renjie a fatal blow at a critical moment.
The Empress Wu is not a righteous person in the tidbits of this drama, in fact, the director of this drama has said a lot of things, first of all, everyone may think it is strange to watch this one, many cases can be closed without evidence, the reason is because the author is a foreigner, and their thinking still belongs to the kind of Sherlock Holmes reasoning case, and then draw conclusions, rather than asking for any human and physical evidence, for example, the previous Yushi case is very classic.
And the director said that after the adaptation, the detective logic of this drama is still the direction of reasoning, and the core of this drama is actually the position of the party that pursues the rule of law represented by Di Renjie and the chivalrous position of the pursuit of happiness and revenge led by Hei Yan. Determining whether a person is guilty or not without evidence in many things is too subjective, and it is not as upright as Black Flame.
More importantly, Di Renjie is loyal to Empress Wu, and is Empress Wu really a righteous person? We don't discuss the historical ones, only the drama version, in the Fengyin case, she set up a bureau to let Changsun Qing and Wei Wujian enter the game, but she is unscrupulous in order to eradicate dissidents, palace maids, He Dajing, four Yu Linwei, etc., do these people's lives deserve to be sacrificed and die tragically?
Obviously not, it can't be said that her new policy is good, so she can sacrifice the lives of others at will, if Di Renjie wants to stand on the position of justice, then he needs to be fair and fair, not because of the martial queen and no longer pursue the death of his friend, as well as the death of many innocent people.
Di Renjie and Cao An's ending is unpredictable Cao An is most likely to be a person with Black Flame, and it can be seen that Cao An is actually likely to like Black Flame, but she and Di Renjie are a bit like playing on the spot, Di Renjie played hooligan to Cao An before, to be honest, there was some obscenity, but later it was a little serious, Di Renjie began to pursue Cao An, and it is still unknown whether Cao An showed true feelings or false intentions.
But whether it is from the perspective of tidbits or reasoning, the ending of Di Renjie and Cao An is unpredictable, and there is a high probability that they will end up with a tragic ending, especially Cao An, who is likely to end up with a tragic death, which is embarrassing. And even if Cao An survives in the end, the possibility that she, the daughter of a criminal minister, will be with Di Renjie is very small.
To sum up, Cao An's identity is likely to be Black Flame's person, she approached Di Renjie for a purpose, and may even help Black Flame go undercover by Di Renjie's side, the relationship between Black Flame and Di Renjie is not ordinary, Di Renjie has been tracking down Black Flame, just to find out the truth about his father Di Zhixun's death.
Even in this process, Di Renjie and Cao An fell in love with each other, but due to the existence of Black Flame, the existence of the Empress Wu, and the identity of Cao An's daughter of a criminal minister, the possibility of being with Di Renjie is very small, and it will mostly end in tragedy.
Of course, as a bystander, I still hope that Di Renjie and Cao An can have a good ending in the end, and I hope that Di Renjie can solve the truth of Di Zhixun's death, as well as solve the mystery of his life experience, and find out all the mysteries.