'Chess board' Intro
When The Avengers was bought by the ABC network in the United States in 1966, network executives were concerned that the audience might not take to the show if it didn't understand the characters, so they commissioned a short introductory sequence to fill in the perceived gap. The sequence was only ever broadcast in the USA, so when Canal+ remastered the episodes, it was omitted from the DVDs produced for the US market. A&E and Canal+ were surprised at the uproar this caused, so when the Emma Peel episodes were repackaged after the Ian Hendry episodes came to light, it was included as a feature on the disc.
I've transcribed the entire script.
CU an ornate dagger sunk into the middle of a target 
PULL OUT to reveal it's in the middle of a waiter's back,
the target painted on his white blazer in black.
He falls to the ground dead
CUT TO wide shot of a chess board with a black king surrounded by a white knight and white bishop, two figures walk onto the board 
- MRS PEEL from TOP STAGE RIGHT, STEED from TOP STAGE LEFT.
They both march diagonally towards the waiter.
"Extraordinary crimes against the people, and the state have to be avenged by agents extraordinary"
STEED bends down to take the champagne bottle from the waiter's hand. 
C/U STEED's hand, as he rises again
"Two such people are John Steed"
HOLD HIM C/U FACE
STEED examines the bottle, then looks intently at EMMA 
CUT TO MID C/U of EMMA's boot
She slips her gold-plated revolver into it 
SLOW PAN up her long legs
CUE V/O as the pan reaches the waist
"And his partner, Emma Peel, talented amateur"
HOLD on EMMA's face, she smiles 
CUT TO C/U two flutes being filled with champagne
"Otherwise known as The Avengers"
ZOOM OUT from glasses to reveal STEED and EMMA
They toast each other and take a sip form the glasses 
They turn away from camera and walk off towards TOP STAGE RIGHT
CUT TO long shot of board, (new angle) FROM BOTTOM STAGE LEFT 
FADE TO BLACK. F/U OPENING OF EPISODE.
|John Steed||Patrick Macnee regular New Avengers 007|
|Emma Peel||Diana Rigg regular New Avengers 007|
|Teleplay by||Brian Clemens regular New Avengers Dangerman The Champions The Professionals Adam Adamant|
|All characters and events in this Teleplay are fictitious. Any similarity to actual events or persons, living or dead, is purely co-incidental.|
|Produced by||Juilan Wintle regular|
|In Charge of Production||Albert Fennell regular New Avengers The Professionals|
|Music by||Laurie Johnson regular New Avengers The Professionals Jason King|
|Associate Producer||Brian Clemens regular New Avengers Dangerman The Champions The Professionals Adam Adamant|
|Photography||Lionel Banes regular The Saint (billed as Lionel Banes B.S.C.)|
|Production Manager||Geoffrey Haine regular The Champions|
|© Associated British Productions Limited MCMLXVI|
|Diana Rigg's wardrobe designed by||John Bates regular|
|and her shoes by||Edward Rayne regular|