This cartoon by Matt from The Daily Telegraph blends two news stories: the release of the Margaret Thatcher biopic The Iron Lady, and the metal theft crime wave in the UK. (According to The Daily Telegraph, more than 1,000 offences are taking place every week as it becomes the "crime of choice" among thieves desperate to cash in on record metal prices.)
A man is shown at the cinema box office wanting to buy a ticket to see The Iron Lady. However, the film has been cancelled, because, as the ticket-seller tells him, "It's been stolen by metal thieves".
The joke is that iron is a metal (Fe in the periodic table).
LANGUAGE
1. A thief is a person who steals something from another person.
2. The plural of thief is thieves.
3. Steal is an irregular verb: to steal, stole, stolen.

