Ruthless death fell on the planets of the Star Federation from a space inaccessible to earthly spaceships. Unknown creatures threaten the destruction of the frontier civilization, which was previously reliably fenced off from everyone by a space barrier. The appearance of a common enemy forced the inhabitants of the Front to enter into an alliance with the earthlings. At their suggestion, the most dangerous ambassadorial mission to the forbidden planet is entrusted to spacefleet lieutenant Oleg Severtsev.