Complex sentence: He went back to his Leningrad family members, but ended up deserting again: stealing his brother-in-law's authentic police uniform, Ilyin left on an unannounced, solitary journey to Moscow.
Split into simpler sentences: He went back to his family in Leningrad; there he stole his brother-in-law's authentic police uniform. Ilyin then left on an unannounced, solitary journey to Moscow.