I think the producers wanted this story to be both sentimental and hard hitting. To me it came across as strange and nonsensical.
Johnny and Mary Kelly along with their young daughter Sara are on the stagecoach. Johnny is betting and losing money to card sharp Ben Marble.
Luke Perry checks on his horse, one of them needs a rest. This upsets Johnny who tries inexplicably to shoot Perry dead. Only Perry gets him first.
It is deemed as self defence. A distraught Mary then leaves her child to Luke to look after. Even though she blames Luke for killing her husband.
Eventually little Sara bonds with Luke even though she saw him kill her dad. Meanwhile Mary has gone of with Ben Marble into a life of prostitution and drink.
As time goes by Simon Kane tells Luke he needs to formally adopt Sara. Luke wants to check on her mother first, to make sure she is happy about it and whether she could be sobered up.
Ben Marble though is not happy, he views Sara as his property.
It is a pretty flawed story. Ben wants Sara but for a life of prostitution, to sell to other men in saloon bars. A man who always calculate the odds. Yet he gets involved in a gunfight with Luke.