Maria Gibson is the main antagonist of the Sherlock Holmes Story "The Problem at Thor Bridge"
The wife of Neil Gibson, the gold king. A very rich American man, who made his fortune in gold. Maria and Neil married when she was young in Brazil, however as she got older and lost her looks, it became clear that they had nothing in common and Neil began to loose his interest in her while she remained devoted to him, this led to him treating his wife very badly.
Neil's attentions instead turned to a Miss Grace Dumbar, the governess of there children. However while Grace rejected his romantic advances and made that very clear she did. She was willing to use her influence over him to have him donate large amounts of his fortune to charities.
Consumed with envy at her influence over and attention from her husband, Maria formulated a plan for revenge. Taking a pair of revolvers she discharged a single shot of one and then had it hidden in Miss Grace's wardrobe. Then sent her a message to meet her at Thor bridge. Miss Dumbar in turn sent a message in reply, which Maria kept hold of. Upon Grace arriving she angrily turned on her, and let out her full fury, sending her away. Then using a piece of string tied to a rock, she had the gun go off killing her and pulling the murder weapon into the river. Thus incriminating Grace for her murder.
Worried by these events, Neil Gibson went to Sherlock Holmes with the case. Holmes immediately spotted several problems in Grace killing Marie, and upon investigating, noticed a chip in the stone work where the bullet had ricochet. Realizing what must have happened he held a test with Watson's own revolver and proved that it was Miss Gibson who killed herself, to incriminate Miss Dumbar.