Answer:
The two things that occurred which resulted in Holmes and Watson’s visit to Dartmoor are the mysterious disappearance of Silver Blaze, the great race horse and the horse trainer's murder. John Straker was the horse trainer who was murdered.
Step-by-step explanation:
"Silver Blaze" is one of Sherlock Holmes short stories which focused on the disappearance of the race horse and the murder of the trainer. Holmes and Dr. Watson visit Dartmoor in order to investigate the case.
This adventurous short story was written by Arthur Conan Doyle.