Season 4 Episode 8
"Burden of Blood"
A lady is asphyxiated to death, and Holmes and Watson find out that she was pregnant and her husband was sterile. This leads to further complications including her family history; meanwhile Holmes helps Detective Bell who needs some financial support for his mother.
Watson and Sherlock investigate the strangulation of a woman in her car.
Sherlock assists Detective Bell in studying for his police sergeant’s exam.
Sherlock surprises Detective Bell with a reward for his excellent work on the case.