In Whitehorse, Yukon, Alex signs on with Manitoulin Transportation and is immediately dispatched to take a load of badly needed food to Inuvik.
His truck stops working not long after he begins the 500-mile run up the Dempster Highway, but it soon starts again and he eases onto the river crossings to complete his delivery.
In Fairbanks, Carlile must transport 70 loads of rig parts up to Prudhoe Bay within 10 days to get the oil fields' exploration efforts started.
Austin voices displeasure not only at Jack's cautious pace due to his oversized load, but also at his decision to stop at Coldfoot for the night when the weather worsens.
In Manitoba, Hugh and Rick negotiate slushy roads, a half-thawed river crossing, and a low bridge before reaching Berens Point.
Based on Phil's disapproving assessment, Ronald is assigned to make another training run, this time carrying a load of pipes with Tony riding along.
After he causes two delays, first with a leaky air line and then by pulling his truck loose from its trailer, Phil sends him back to Fairbanks and wonders whether he is qualified to drive the Dalton.
In Fairbanks, Austin picks up an excavator for his first solo run, while Jack voices his concerns to the Carlile bosses about the rookie's driving habits.
In Fairbanks, Ronald returns to duty but bristles at his next assignment: delivering a load of dog food to the downtown area for the start of the Yukon Quest dogsled race.
A road crew pulls him loose with a snowblower, allowing the traffic jam behind him to start moving, and he delivers his load to Prudhoe and heads south.
They are forced to abandon the loads and head back to Winnipeg; along the way, Rick gets briefly stuck in a snowbank until a passing motorist pulls him loose.
Meanwhile, Alex fights through a late rendezvous, bad weather, and slick uphill runs to pick up a load of groceries and deliver it to Inuvik before the road becomes impassable again.
In Fairbanks, Carlile owner Harry McDonald and terminal manager Lane Keator head north with loads of explosives to make up for Jack's continuing absence.
In Fairbanks, Ronald starts his first solo run with a load of supplies needed in the village of Manley Hot Springs, a new destination for Carlile deliveries.
Austin and veteran Carey Hall are called in to help with a heavy haul mission, a 100-ton modular building that must reach Prudhoe within 72 hours.
The crew loses time due to maneuvering problems on the road leading to the Dalton, then again when one truck develops brake trouble.
Darrell picks up a load of sheet rock and heads north, making good time until he finds a jackknifed truck blocking the road.
With a relief driver taking Carey's place in the lead for the heavy haul convoy, Austin makes a driving mistake that has the potential to send all three trucks into the ditch.
On a steep uphill turn, he slides badly and spins out; an oncoming truck nearly hits him as he scrambles to chain his tires in the middle of the road.
The next morning, Darrell hits an extremely bumpy stretch and must slow down to spare his trailer before reaching Prudhoe; he then picks up a bus for the return to Fairbanks.
He picks up a shack several feet longer than his trailer and hauls it back to Winnipeg, noting the extent to which the road is melting down.
Jack and Austin head north from Fairbanks (respectively taking lumber and a pickup truck, and long overhead crane beams), trying to deliver their loads before the shutdown.
The length and weight of Austin's load give him difficulty on the uphill runs when he decides not to chain his tires, causing delays for himself and the southbound drivers.
With 10 days left in the Alaska ice road season and Prudhoe reopened after the cold-weather shutdown, drivers are hurrying to move all the loads they can.
Once they reach Nuiqsut, Jack offloads his fuel quickly; Darrell, though, must deliver his cargo around town and then load some pickup trucks onto his flatbed for the return trip.
Ray takes a load of pipes up from Fairbanks and makes good time into the evening, successfully climbing an uphill stretch where he went into the ditch two years earlier.
In Inuvik, Alex picks up a load of firewood and supplies needed in Tuktoyaktuk and starts onto the cracked, weakened ice of the Arctic Ocean.
In Fairbanks, Jack and Darrell each pick up loads that must reach Prudhoe by the end of the day: oil rig parts and pipe elbows, respectively.
Jessee (seasons 3 and 4) returns to drive the Dalton along with three newcomers, and Hall appears in one episode to help move a modular building up from Fairbanks.
Additionally, both Molesky and Kromm independently monitor other drivers' standards and behavior, and advise Fairbanks Terminal Manager Lane Keator if there are issues like those that led to Redmon and "Porkchop" being fired.