Choc-o-BoCo! is a magazine story.
BoCo was helping the workmen to make a brand new tunnel in the hillside by taking away truckfuls of unwanted soil. But, one day, it started to rain and the earth in BoCo's trucks turned to mud. The trucks did not like it either, they bounced about sending mud flying all over BoCo. The other engines stared when BoCo returned to the Main Station and after being washed, he was the last one back to the sheds.
During the night, it rained heavily and the next morning, when BoCo was on his way to collect more discarded soil, he ran into a landslide and was covered in thick, brown mud again. Luckily, BoCo wasn't hurt, but he did need another hard scrubbing. Later, the Fat Controller sends BoCo to collect some goods from a factory. BoCo slowed down to enter the factory siding, but he jumped right off a loose rail and smashed his way through the big, wooden factory doors. Inside, he hits an enormous tub of sticky, brown goo. It splashed all over BoCo's face as he grinds to a halt.
At last, a factory crane lifts BoCo back onto the track and he limps home. Just as a guard prepares to give BoCo a good scrubbing, BoCo stops him. BoCo sticks out his tongue and licks some of the goo off his face. The other engines gasp; thinking that the messy diesel had just eaten mud. BoCo laughs and tells them all it is actually chocolate!
- This story's plot has some similarities to the sixth season episode, Percy's Chocolate Crunch and the magazine story Sweet Scent.
- Part of this story was rereleased in a 2003 Thomas and Friends magazine story puzzle under the name of BoCo's Bathtime!.
- The title for the story does not capitalise the "C" in BoCo. The title presumably relies on BoCo being pronounced incorrectly as "Boco".