Curse of the marriage contract

Dina Reznikova followed along the usual route - a night train to Moscow, where she worked as a translator in the negotiations. Her neighbor was a dead drunk type, scattering things over the compartment. Gathering them, Dina noticed an old document in an incomprehensible language, but at that moment she did not attach importance to him, because soon her childhood friend Boris Posadsky appeared in the compartment, who was also heading to the capital. And in the morning, Dina discovered that she had lost her passport, and instead of the hotel she stopped at Boris"s rented apartment. But this turned out to be not the most important nuisance - returning home in the evening, she literally stumbled upon a dead man lying on the landing! It was their night fellow traveler, but how did he get here and who killed him?