Sherlock in Serbia is reference to which actual novel?

After Sherlock returning London, Mycroft told him that

Yes. You got yourself in deep there (Serbia) with Baron Maupertuis.

Now some googling and got that

On Monday, February 14, 1887, Sherlock Holmes begins his two-month-long investigation of Baron Maupertuis and the Netherland Sumatra Company, spending over fifteen hours a day working on the case (including one five day marathon of detection). [source]

also

Baron Maupertuis is associated with a Netherland-Sumatra¹ Company. Now I think that company is in Serbia. That's how Sherlock get occupied in Serbia.

So maybe the incident is loosely referring to The Squire of Reigate.

¹

Later we came to know that bomb had been planted at Sumatra Road railway station. So maybe another loosely bound reference!

I couldn't think of any story with the Serbian incident in Doyle's books, the ones that caught my attention are 2 direct homages to The Adventure of the Empty House which was the first short story in the category Return of the Sherlock Holmes.

One was the incident with the old patient with Russian Accent who speaks to John who shows those dvds, the names on those dvds were all the names of the books sherlock carried disguised as an old book seller in that story and the humor where John tries to unmask the old man was a reference as well.

Secondly the name of the villain on this episode Lord Moran who is also named after Colonel Sebastian Moran who was one of moriarity's right hand henchman as well as an excellent shot who gets captured by Sherlock and Watson in that story.