On his way home during a snowstorm, Toby is flagged down by Farmer McColl. His sheep are due to give birth soon and he needs a vet urgently to check on them. Toby goes to the next signalbox where his driver telephones for a vet.
Toby arrives at the station where the Fat Controller is waiting with the vet. The vet climbs aboard Duck's footplate and Duck sets off to rescue the sheep with his snowplough. However, the snow is now much thicker and the tracks are blocked. Duck cannot go on, so he returns to the station. Toby suggets using his old line to get to Farmer McColl's, but the Fat Controller knows that Toby's old line cannot take Duck's weight. Toby insists that he should go as he knows the old line and they have got no other choice. So the vet clims aboard Henrietta and the Fat Controller warns Toby to be careful.
Toby sets off, full of confidence. However, he soon realises that there is something he forgot about - the rickety old bridge spanning a deep gorge. Slowly, Toby pulls Henrietta across the old bridge, which creaks and groans under his weight. Toby is scared, but determined to cross it just for the sake of the sheep. Once across, Toby soon reaches the farm and Farmer McColl is delighted to see them.
The vet and Farmer McColl check the newly-born lambs, but they need warmth and comfort. Toby explains that Henrietta can provide that, so the sheep and lambs stay inside Henrietta until the snow thaws.
- It is said that the lambs were with Henrietta, but a close up shows the red coaches.