"Longmire" season 4 ended with Walt (Robert Taylor) and Dr. Donna Monaghan (Ally Walker) getting intimate in the former's home when an intruder suddenly broke in. According to a report from Cartermatt, it is now likely that this unidentified intruder is none other that Walker Browning (Callum Keith Rennie). 

The report points out that Browning already has the motive to attack, given that Walt was responsible for ending his whole operation, which means Browning may be out for revenge. It is also pointed out that Browning was suddenly missing from his hospital bed, indicating he left in a hurry and is now out hunting for Walt.

However, the report points out that there are two complications with this theory. First, it would require Browning move pretty quickly and the season 4 finale did not show Browning executing his plan with haste. The second problem would be that Browning showed no previous knowledge of Walt's residence, so it would take time for him to locate Walt and then eventually get there.

It is also pointed out that someone must have helped Browning get out of the hospital and locate Walt, which is why one of the most popular suspects is Dr. Monaghan herself. It was previously reported that she may be working together with Browning all this time, being his informant and accomplice.

This would resolve some of the issues mentioned. Monaghan would be able to inform Browning where Walt is, when he's vulnerable and when the proper time to attack unfolds. Her actions toward Walt in the burning van is also deemed questionable.

In the original novels, Walt is romantically involved with Vic (Katee Sackhoff) but this has yet to happen on the show. It is speculated that his relationship with Monaghan will not last long, given that she may be an antagonist, allowing Walt to be free once more in order to form a relationship with Vic in the future.

"Longmire" season 5 is currently in production and is expected to premiere by September on Netflix.