'Trojan Horse' by Malcolm Hulke

Steed is assigned to look after the security of a shah's horse, which is currently in England for a season of races. The horse is lodged at the Meadows Stables, where Steed discovers that the owner, George Meadows, owes a bookie named Heuston a considerable gambling debt, run up after Meadows bet on his own horses. Meadows is unable to speak out without causing himself to be ruined, and so Steed sends Mrs. Gale to get an executive position with the criminal's business front. Together they uncover an assassination service in which jockeys use special binoculars with built-in poison-dart guns to silently dispatch the desired target in public…

Patrick Macnee (John Steed), Honor Blackman (Cathy Gale), Basil Dignam (Major Ronald Pantling), T.P. McKenna (Tony Heuston), Derek Newark (Johnson), Arthur Pentelow (George Meadows), Geoffrey Whitehead (Rt. Hon. Lucien ffordsham), Lucinda Curtis (Ann Meadows), John Lowe (Lynton Smith), James Donnelly (Kirby), Marjorie Keys (Tote Girl)

Directed by Laurence Bourne
Produced by John Bryce

TX:
UK: 8th February, 1964

Notes:
*Featuring John Steed and Mrs. Cathy Gale