Highlights from the Fourth Episode of Season 2

A woman from Sherlock’s (Jonny Lee Miller) past emerges as a possible suspect when the CEO of a financial consulting company is poisoned to death. Photo: Patrick Harbron /CBS ©2013 CBS Broadcasting, Inc. All Rights Reserved

A woman from Sherlock’s (Jonny Lee Miller) past emerges as a possible suspect when the CEO of a financial consulting company is poisoned to death. Photo: Patrick Harbron /CBS ©2013 CBS Broadcasting, Inc. All Rights Reserved

Holmes (Jonny Lee Miller, left), Watson (Lucy Liu, middle) and Gregson (Aidan Quinn, right) are called upon to track down the person who poisoned the CEO of a financial consulting company. Photo: Patrick Harbron /CBS ©2013 CBS Broadcasting, Inc. All Rights Reserved

Gregson (Aidan Quinn) must track down the person responsible for poisoning the CEO of a financial consulting company. Photo: Patrick Harbron /CBS ©2013 CBS Broadcasting, Inc. All Rights Reserved

Holmes (Jonny Lee Miller) is called upon to track down the person who poisoned the CEO of a financial consulting company. Photo: Patrick Harbron /CBS ©2013 CBS Broadcasting, Inc. All Rights Reserved

Holmes (Jonny Lee Miller) is called upon to track down the person who poisoned the CEO of a financial consulting company. Photo: Patrick Harbron /CBS ©2013 CBS Broadcasting, Inc. All Rights Reserved

Gregson (Aidan Quinn) must track down the person responsible for poisoning the CEO of a financial consulting company. Photo: Patrick Harbron /CBS ©2013 CBS Broadcasting, Inc. All Rights Reserved

Holmes (Jonny Lee Miller, left) and Watson (Lucy Liu, right) are called upon to track down the person who poisoned the CEO of a financial consulting company. Photo: Patrick Harbron /CBS ©2013 CBS Broadcasting, Inc. All Rights Reserved

A woman from Sherlock’s (Jonny Lee Miller) past emerges as a possible suspect when the CEO of a financial consulting company is poisoned to death. Photo: Patrick Harbron /CBS ©2013 CBS Broadcasting, Inc. All Rights Reserved

Sherlock (Jonny Lee Miller) encounters a woman from his past while investigating a murder. Photo: Mark Schafer /CBS ©2013 CBS Broadcasting, Inc. All Rights Reserved

Sherlock (Jonny Lee Miller, right) encounters Anne Barker (Laura Benanti, left), a woman from his past, while investigating a murder. Photo: Mark Schafer /CBS ©2013 CBS Broadcasting, Inc. All Rights Reserved

Sherlock (Jonny Lee Miller) encounters a woman from his past while investigating a murder. Photo: Mark Schafer /CBS ©2013 CBS Broadcasting, Inc. All Rights Reserved

Sherlock (Jonny Lee Miller) encounters a woman from his past while investigating a murder. Photo: Mark Schafer /CBS ©2013 CBS Broadcasting, Inc. All Rights Reserved

A woman from Sherlock’s (Jonny Lee Miller) past emerges as a possible suspect when the CEO of a financial consulting company is poisoned to death. Photo: Mark Schafer /CBS ©2013 CBS Broadcasting, Inc. All Rights Reserved

A woman from Sherlock’s (Jonny Lee Miller) past emerges as a possible suspect when the CEO of a financial consulting company is poisoned to death. Photo: Mark Schafer /CBS ©2013 CBS Broadcasting, Inc. All Rights Reserved

Sherlock (Jonny Lee Miller, left) encounters Anne Barker (Laura Benanti, right), a woman from his past, while investigating a murder. Photo: Mark Schafer /CBS ©2013 CBS Broadcasting, Inc. All Rights Reserved

Sherlock (Jonny Lee Miller, left) encounters Anne Barker (Laura Benanti, right), a woman from his past, while investigating a murder. Photo: Mark Schafer /CBS ©2013 CBS Broadcasting, Inc. All Rights Reserved

Watson (Lucy Liu) is called upon to track down the person who poisoned the CEO of a financial consulting company. Photo: Patrick Harbron /CBS ©2013 CBS Broadcasting, Inc. All Rights Reserved