Based on

Movies like Musicians of the Same Regiment (1965)

The invaders are leaving the northern town of the young Soviet republic. The brave underground activist Alexei Ilyutinsky infiltrates a musical troupe organized to entertain the White Army command and boost the morale of the population. The new horn player, who has no musical ear whatsoever, passes on the White Army's defense plan to the Reds and saves Bolshevik Makeev, the former chairman of the provincial executive committee, from being shot.