"I pay homage to ISIS. To listen and obey. God is a witness to what we are saying. Praise God!" The ISIS leader shouts and the crowded town square answers. It gives a startling indication of ISIS's control of Syria's Northern Front. It's too dangerous for the cameraman to film, so a local man films it secretly. Muhammad Ali - a Syrian and one of only a few reporters to make it safely into this region in recent months - gives us a gripping insight into the battle raging between the FSA and ISIS from inside the country. "If a group wants to use weapons against us, fight us, and their goal is to steal the Syrian revolution, we will not hesitate to fight back", Jamal Marouf, an FSA leader says as he explains why they are now fighting ISIS as keenly as the government forces. We see the FSA engage ISIS in direct combat, forcing them to abandon one of their bases and reclaim the town of al-Atareb. The local response gives an indication of how ISIS are feared here: "Since we were freed we live in safety. ISIS hobbies include sabotage, kidnap and murder in cold blood", one townsman tells us. A fascinating insight into Syria's fractured "war within a war".