"У.Е." means "условная единица" in Russian or "CU" (conventional unit) in English. A conditional unit is a euphemism used in Russia to denote a monetary amount in a foreign currency (usually US dollars) or an equivalent amount of a dollar in rubles at an official or exchange rate.
The retired 50-year-old FSB colonel at his own risk and continues to investigate the case, because of which he was sent to retirement, and is drawn into a swirl of events related to the leakage of Russian capital abroad and the fight against international terrorism.