Поставить в нужную форму incredible as may seem, it (contain) strange being who are believed to be part of an army from

Incredible as may seem, it contained strange beings who are believed to be part of an army from the planet Mars. Soft music followed. A subtle touch to get people anxious. What was going on? The announcer came on again. There was a nervy, panicky tone to his voice. He said the situation was changing rapidly.