Published in the TV Century 21 Summer Extra, 1965.
When a major Bereznik assassin is spotted arriving in London, Lady Penelope is certain he is in the City to kill someone but the question is who. Following him, she will discover a plan to kill the World President himself.
Note: the original release has the first two pages in black & white and the last two in color. When it was reprinted in Thunderbirds: The Comic Collection in 2013, the first two pages were colorized.