The Doctor, Jamie and Zoe arrive on Earth at a time when all transportation is conducted via T-Mat, a matter teleportation system operated from the Moon. The TARDIS materialises in a museum owned by Eldred, who resents T-Mat for rendering rocket technology obsolete. When the Ice Warriors invade the Moon, the humans manage to stall their plans by disabling T-Mat. The time travellers volunteer to journey to the control station aboard a rocket which Eldred has maintained. But it's just a matter of time before the Ice Warriors repair T-Mat, and use it to launch a global assault with deadly alien seed pods.

Shortly after the broadcast of The Ice Warriors at the end of 1967, Doctor Who producer Peter Bryant sought a new story featuring the eponymous Martians from their creator, Brian Hayles. His motivation was twofold: the Ice Warriors had been a popular addition to the programme's monster menagerie, but their costumes had also been very expensive and a return appearance would better justify the cost. Hayles developed “The Lords Of The Red Planet” during the first part of 1968, but it appears that the Doctor Who production team eventually soured on it, and a new storyline was commissioned from Hayles on July 15th. Entitled The Seeds Of Death, it proved more acceptable, and the scripts were subsequently requested on August 28th.

At this stage, Hayles deviated from his story breakdown in several respects. Kelly was originally a man, assisted by a woman named Mary Burcott; with the former changed to the female Gia Kelly, Mary became the male Brent. It had been intended that both Mary and Eldred would accompany the TARDIS crew to the Moon via the rocket. The Martian warlords were envisaged as being more humanoid than their Warrior brethren, and Episode Two would have introduced Slaar's superior, named Visek. The Martian spores were only intended to erupt after four weeks rather than almost instantaneously, and were initially destroyed by concentrated oxygen -- possibly in a liquid form -- instead of water.

Brian Hayles was asked to replace Jamie McCrimmon with a new companion named Nik

Around the time that the scripts were commissioned, Hayles was asked to implement a major change by replacing Jamie McCrimmon with a new companion named Nik. Frazer Hines had decided to leave Doctor Who in the story preceding The Seeds Of Death but, during September, his status became less certain: it appears that Hines changed his mind several times, leading Hayles to write the role of the male companion for an unspecified character. Finally, it was confirmed that Hines would, in fact, be remaining on Doctor Who until the end of the season, so that he could leave alongside Patrick Troughton. As such, Hines agreed to a contract for The Seeds Of Death on October 9th.

On October 10th, Hayles delivered the last of his scripts for The Seeds Of Death, only to learn that the production team had several concerns about his work. The writer explained that the uncertainty over Jamie's inclusion had caused him difficulties, as had a request to adapt his storyline to exclude the Doctor from Episode Four, so that Troughton could avail of a week's holidays. The BBC countered that script editor Terrance Dicks had provided him with ample warning on both counts. Hayles took a stab at rewriting The Seeds Of Death but, by the end of October, it had been decided that Dicks would redraft the final four parts. Formal approval to do so came retroactively, on December 13th. Although Dicks was apprehensive about overhauling Hayles' scripts to such a large extent, he was relieved to learn that writer was very understanding about the situation.

One of the major changes Dicks effected was the removal of a subplot from Episodes Three and Four, in which Kelly was mind-controlled by the Ice Warriors. He also added the element of the Martian fleet, led by the Grand Marshall, to the concluding installments. It was originally planned to have four standard Ice Warrior costumes available for The Seeds Of Death -- excluding the new suits built for Slaar and the Grand Marshall -- but this was reduced to three in order to cut costs. A late change saw the removal of a line in which Eldred revealed that his rocket had achieved the first manned Moon landing; this was altered to account for the likelihood that NASA would soon accomplish the same feat -- as, in fact, they did on July 20th of the following year.

The director assigned to The Seeds Of Death was Michael Ferguson, who had last handled on The War Machines three years before. His work began on December 13th, with model filming at the BBC Television Film Studios in Ealing, London. After the weekend, live action filming took place at Ealing from December 16th to 18th, for sequences set outside the Weather Control Bureau. A single location day followed on the 19th. Taking place at Hampstead Heath in Hampstead, London, the principal concern was the material involving the Ice Warrior abroad in the city. Remaining in costume while taking a break, actor Steve Peters surprised a passing motorist so much that she suffered a minor traffic accident. Two more model days at Ealing, on December 20th and 23rd, completed the pre-filming.

According to the normal Doctor Who production pattern, studio recording should have begun on December 27th. However, Episode One was delayed until January 3rd, 1969 due to the Christmas holidays. As usual, all six installments of The Seeds Of Death were recorded on consecutive Fridays at Lime Grove Studio D in Shepherd's Bush, London. Throughout the production, Ferguson made use of out-of-sequence recording, especially on Episodes Two and Three. Troughton was absent when Episode Four was taped on January 24th, and production wrapped up on February 7th. Exactly a month earlier, on January 7th, stories appeared in the press which announced that the lead actor would be leaving Doctor Who in the summer. The era of the Second Doctor was nearing its end...

• Doctor Who Magazine #274, 10th February 1999, “Archive: The Seeds Of Death” by Andrew Pixley, Panini UK Ltd.
• Doctor Who Magazine Special Edition #4, 4th June 2003, “Paradise Lost” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who: The Complete History #14, 2018, “Story 48: The Seeds Of Death”, edited by John Ainsworth, Hachette Partworks Ltd.
• Doctor Who: The Handbook: The Second Doctor by David J Howe, Mark Stammers and Stephen James Walker (1997), Virgin Publishing.
• Doctor Who: The Sixties by David J Howe, Mark Stammers and Stephen James Walker (1992), Virgin Publishing.