The Doctor, Polly and Ben find themselves on the Cornish coast in the 17th century. The Doctor is the lone witness to the dying words of a former pirate, who wishes to pass on the location of a buried treasure. Soon, however, the time travellers are pursued by the vicious Captain Pike, who is also in search of the treasure, and become embroiled in the covert smuggling operations of the era.

On March 8th, 1966, some months after he completed work on The Celestial Toymaker, Brian Hayles was commissioned to write a storyline for a Doctor Who adventure entitled “The Nazis”. Shortly thereafter, however, story editor Gerry Davis contacted Hayles with a request that he shift his attention to a new serial which needed to be completed at very short notice. Davis requested that this be a high-adventure historical, and so Hayles suggested a plot in the vein of Russell Thorndyke's Dr Syn novels, which dealt with pirating and smuggling in the seventeenth century. Davis concurred, and The Smugglers was commissioned on April 4th; “The Nazis”, meanwhile, would eventually be abandoned on June 15th.

The Smugglers, designated Serial CC, was scheduled to be the final story made as part of Doctor Who's third production block, but would be held over to start the programme's fourth season. To properly realise Hayles' swashbuckling tale, The Smugglers was assigned Doctor Who's first major location shoot. To date, the handful of stories which featured any out-of-studio filming at all had been confined to the vicinity of London; The Smugglers, by contrast, would enjoy five days in Cornwall.

To this end, Julia Smith was named as the serial's director. Smith had earned her start at the BBC as a production manager before joining Paddy Russell -- who had helmed The Massacre Of St Bartholomew's Eve -- amongst first women to take the BBC's internal directors' course. She had since handled episodes of programmes including Dr Finlay's Casebook and Compact. Smith knew the Cornish coast very well, and therefore could help ensure a smooth period of filming. In particular, Smith had to exercise care with regard to William Hartnell. The star's health was getting worse as the production block drew to a close, and he had recently suffered through several months of poor relations with the previous production team of John Wiles and Donald Tosh, who left Doctor Who in January. To make matters worse, Hartnell was finding it difficult to mesh with his new co-stars, Michael Craze and Anneke Wills. Craze and Wills were set to join Doctor Who in The War Machines, the serial immediately preceding The Smugglers.

Due to the number and complexity of the fight sequences in The Smugglers, Smith sought the assistance of stuntman Derek Ware. Ware had worked on Doctor Who since 100,000 BC, and had recently formed his own stunt agency, called HAVOC. Ware and his HAVOC team would prove to be an integral part of Smith's production, marking the start of a relationship with Doctor Who which would continue well into the Seventies.

On June 18th, cast and crew travelled to Penzance, their base of operations for the location work. Throughout the next five days, Smith's team would be assisted by numerous local extras, notably members of the Sea Cadets. Hartnell, Craze and Wills were required only for the first day of filming, June 19th, at Nanjizal Cove south of Land's End; worked continued there on the 20th, which also took in material at nearby Bosistow Cliffs. June 21st saw the team move to St Grada Church in Grade, Church Cove, and the environs of the town of Helston, while Trethewey Farm in Trethewey was the venue for the 22nd. All the scenes recorded on June 23rd were set aboard the Bonny Mary, the ship which doubled for the Black Albatross. The vessel departed from Newlyn Harbour and anchored off Nanjizal Bay. Several of the cast and crew suffered from seasickness on this day -- including Smith herself -- but managed to pull through and complete all the necessary material.

Studio recording took place in Riverside 1 on successive Fridays beginning on July 8th. On this day, Terence De Marney, playing the Churchwarden, unfortunately misrecited the riddle which would form a key element of the narrative; instead of the names “Ringwood, Smallbeer, and Gurney”, De Marney listed “Smallwood, Ringwood, and Gurney”. Taping otherwise proceeded normally until the final episode was recorded on July 29th, bringing an end to both The Smugglers and Doctor Who's third production block.

Meanwhile, producer Innes Lloyd had convinced his superiors at the BBC that Hartnell should be replaced with a new actor early in programme's fourth season. Michael Hordern -- who counted the films Cleopatra and The Spy Who Came In From The Cold amongst his many credits -- was considered for the role, as was Patrick Wymark, who had appeared in programmes such as Danger Man and The Power Game. (Ironically, both Hordern and Wymark had featured in The Scarecrow Of Romney Marsh, a TV adaptation of Thorndyke's Dr Syn novels featuring Patrick McGoohan in the eponymous role.) Another possibility was Ron Moody, star of feature films such as Murder Most Foul and who had recently appeared in an episode of The Avengers.

In late June, however, actor Patrick Troughton was approached by Lloyd. Troughton was reticent to accept the part immediately, but contemplated the offer throughout the month of July. During the production of The Smugglers, Hartnell and Lloyd met and Hartnell agreed that he should leave Doctor Who after one more serial, to be recorded at the start of the new production block. Hartnell had long hoped to complete five seasons of Doctor Who, but now realised that this was an unlikely proposition. He was reassured by the possible casting of Troughton, whom he respected as an actor, and also by Lloyd's assertion that his successor would have a totally new take on the character of the Doctor, rather than simply aping Hartnell's performance.

Hartnell informed his wife, Heather, of his decision on July 16th. The pair then decided to vacation in Cornwall, during which time the news of Hartnell's imminent departure from Doctor Who was announced to the press on August 6th. Just over a month later, the first episode of The Smugglers aired, getting Doctor Who's tumultuous fourth season under way.

• Doctor Who: The Handbook: The First Doctor by David J Howe, Mark Stammers and Stephen James Walker (1994), Virgin Publishing, ISBN 0 426 20430 1.
• Doctor Who: The Sixties by David J Howe, Mark Stammers and Stephen James Walker (1992), Virgin Publishing, ISBN 1 85227 420 4.
• Doctor Who Magazine #321, 18th September 2002, “Archive: The Smugglers” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who Magazine Special Edition #7, 12th May 2004, “Bye Bye Blues” by Andrew Pixley, Panini Publishing Ltd.