BIS is short for Bundesamt für Innere Sicherheit (Federal Office for Internal Security).
This German authority deals with terrorism, counter-espionage, treason, organized crime and also megacorporate activities. The BIS also monitors the German state governments and their loyality to the Federal Government in Hannover.
Work is done mostly by highly trained undercover operatives but in times of need the armed forces of the Bundesgrenzschutz (or any other police) can be requested.
(Unlike the BKA that shares some of its responsibilities the BIS is rather a secret service than a police.)