The Bugbears Descend

While you are with Prudence at the toll cabin, she suddenly speaks out, "we have visitors on the hillside, probably those bugbears again."
In all likelihood, the party will be taken aback at such an interruption. The reality is that part of her defense system involves alarm spells placed around the cabin to alert her to the approach of creatures from a variety of directions. She will attempt to persuade you to go outside and deal harshly with them. As you debate or move to the exit, there is a sudden explosion from somewhere outside.
It turns out that not only does she have alarms placed strategically, she has glyphs set as well. "I have a lot of time on my hands," she offers. When you reach the outside, you note that there is indeed a dead bugbear smoldering on the side of the hill, and two others trying to discreetly disappear into the hills east of the cabin along a worn strip of ground that might be a path.
Prudence feels it is indeed fortuitous that you have found her at this time, and believes fortune has indeed smiled upon her. She offers to refund you 25 gp if you will track the two bugbears into the hills and defeat them. There have been increasing raids from them over the last month, and with traffic slow on the river at this time of year, no one to send into the hills after them. She lost three weeks worth of provisions in the first raids, before she set her defenses, and is running low on supplies. She is certain she can hold out until the next delivery from Aron's Bowl arrives in a week, but not if they launch a successful raid in the meantime.
According to her, they have begun recognizing where the glyphs are placed, and approaching more cautiously. She points out that there are two rings of alarms and glyphs, and that the one that exploded a mere 50 feet from the back of the cabin was in the inner ring. She will show the location of the defenses if the party will help her, and offers them looting rights to whatever they find, other than foodstuffs, which she asks to have returned to her.
On the trail, the party can make periodic Survival checks (DC16) to follow the bugbear path. If they succeed by greater than 5, they can notice that something about the tracks seems odd. If they wish to roll an Insight check (DC15) they can learn that some of the tracks seem to have been deliberately left to be followed.
Eventually, the party reaches an area where a small stream runs down the way they came to their left, and a cliff wall rises steeply to their right. The path seems to run on past the cliff wall to a more gentle slope, then zig-zag to the top. As they start the climb, have them roll Perception checks (DC20) to notice they are surrounded by goblinoids, and in the midst of an ambush. If they all fail, the monsters launch their ambush with surprise.
The rock wall is deceptive. It is actually fractured, with an eight inch thick sliver of rock rising up a foot in front of the rest of the wall, so that the bugbears can run directly up to the top of the cliff via a narrow cleft, completely out of sight of the trail the party is following. The ambush has been set here. There are 6 goblins, 2 bugbears and a hobgoblin waiting in the cleft to swarm out behind the party as they ascend. At the same time, 2 more hobgoblins, 2 bugbears and 4 goblins attack from the path ahead of them. In both instances, the goblins fire spears at the party, while the hobgoblins charge. The bugbears stay back as much as possible to shift their targets more quickly.
If the battle goes against the monsters, the last two will flee pell-mell up and over the hill. The remaining dead can be searched to reveal slight treasure, 50 gp, 3 potions of healing, and several scimitars of usable quality (4). Anyone understanding goblin will hear the escaping creatures vowing to warn the leaders and return in strength. They should be followed and taken.