Article: List of Sherlock Holmes episodes

Question: What dates did "The Sign of Four" and "The Hound of the Baskervilles" aired, respectively?
Answer: "The Sign of Four" and "The Hound of the Baskervilles", aired on 29 December 1987 and 31 August 1988 respectively.
Evidence table:
No.
Title
Based on
First broadcast
Synopsis
14
"The Empty House"
"The Adventure of the Empty House"
9 July 1986
Holmes returns to England, to Watson's shocked surprise, and must stop a member of Moriarty's gang who is trying to assassinate him.
15
"The Priory School"
"The Adventure of the Priory School"
16 July 1986
A rich duke reluctantly allows Holmes to search for his ten-year-old son who is missing from his boarding school along with the German tutor.
16
"The Second Stain"
"The Adventure of the Second Stain"
23 July 1986
The Prime Minister asks Holmes to help recover a stolen letter which could lead to war if released.
17
"The Musgrave Ritual"
"The Adventure of the Musgrave Ritual"
30 July 1986
While vacationing at the estate of his old university classmate Sir Reginald Musgrave, Holmes is called in when the scholarly butler disappears after being discovered reading an old document about a mysterious family ritual.
18
"The Abbey Grange"
"The Adventure of the Abbey Grange"
6 August 1986
Lord Brackenstall has been murdered and his battered wife says that a thief and his sons were the culprits: wine glasses convince Holmes otherwise.
19
"The Man with the Twisted Lip"
"The Man with the Twisted Lip"
13 August 1986
Watson finds Holmes in an opium den, where he has been sent to look for Neville St Clair, who is suspected to have been killed by a beggar.
20
"The Six Napoleons"
"The Adventure of the Six Napoleons"
20 August 1986
Holmes is contacted by Inspector Lestrade after the police are baffled by a series of burglaries serving only to steal and smash identical busts of Napoleon.
21
"The Sign of Four"
The Sign of the Four
29 December 1987
Mary Morstan has received a pearl in the post every year since her father's disappearance; this leads Holmes and Watson to the truth about a secret pact between four convicts during the Indian Rebellion of 1857.
22
"The Devil's Foot"
"The Adventure of the Devil's Foot"
6 April 1988
In Cornwall, Holmes investigates when a woman mysteriously dies with a horrified look on her face and her two brothers are driven insane.
23
"Silver Blaze"
"The Adventure of Silver Blaze"
13 April 1988
Holmes investigates when a prized racehorse goes missing and his trainer is found bludgeoned to death.
24
"Wisteria Lodge"
"The Adventure of Wisteria Lodge"
20 April 1988
An amateur cartographer who stayed with another map enthusiast seeks help when his host vanishes in the middle of the night.
25
"The Bruce-Partington Plans"
"The Adventure of the Bruce-Partington Plans"
27 April 1988
Holmes helps Mycroft when stolen top secret blueprints for a submarine are found on the body of a civil servant found dead on the tracks of the Underground.
26
"The Hound of the Baskervilles"
The Hound of the Baskervilles
31 August 1988
Sir Charles Baskerville was found dead with a horrible expression on his face after seeing a mysterious demonic spirit of a gigantic hound that has haunted his family.