JOSEPH EID / AFP / GETTY IMAGES Syrian army soldiers inspect a house in the village of Western Dumayna, 7 km north of the rebel-held city of Qusayr, on May 13.

The short message screeched over a walkie-talkie, prompting the half a dozen rebels in the room who had been lounging on flat mattresses and drinking tea to jump to their feet, grab their guns and run out of the door.

It was almost 7:30 p.m.

Ten men in civilian garb had just sneaked out of the Syrian army’s Zahlanee checkpoint some 500 m away from the rebel position, just across an olive grove, and were now moving toward a cave on the outskirts of the grove. The cave had been a rebel position at one point.

“They told them not to be late,” the voice over the walkie-talkie said, relaying what he had heard from a transmitter set to intercept Syrian Army communications, “so they’re not defectors. They’re not trying to defect. They’re planning something, but what I don’t know.”

A rebel named Ahmad picked up a BKC machine gun, while others grabbed Kalashnikov rifles. Another rebel, Abu Sammy, manned the 14.5-mm antiaircraft gun mounted on the back of a navy blue pickup truck as his colleagues in the Farouq Brigade bundled into the back.

It sped a short distance down a narrow deserted path closer to the Zahlanee checkpoint, one of two key loyalist positions that protect the larger, fortified Wadi Deif military base. (The other is called the Hamidiyeh.)

The base is one of the last remaining Syrian military outposts in the vast northern province of Idlib. The rebels have been trying to overrun it since at least October as they try to wrest full control of Idlib.

So far, Syria’s rebel forces have not managed to gain full control of any of the country’s 14 provinces.

Find out why, here.