What this is:

Emilia Galotti was a tragic play written by German Enlightenment vanguardist Gotthold Ephraim Lessing during the 18th century that explored and challenged the then-already tenuous notions of relationships between lord and subject, bourgeoise values, and that perennial favourite among dramatists, the threat of sexual deflowerment in the form of rape (I'm glad I finally got your attention).

What it's about:

The plot, set in an anonymous Italian realm, concerns itself with a young girl (the title character) who becomes engaged to be married to a respected count (Appiani). However, this plan is upset entirely when the lovesick Prince learns of her wedding and, galvanized into action by her impending wedding, decides to kidnap her and claim her as his own. A band of hired ruffians is sent to attack the pair's coach and seize Emilia, but the abduction is botched; Appiani is shot dead during the struggle, and Emilia escapes into the forest, only to run straight into the hands of the Prince at his hunting lodge. When her parents learn of her abduction and her fiance's slaying, her father sets out to rescue her, during the course of which the plot reveals itself step by step to him and his daughter. He confronts both the Prince and his captive at the end and, in one of the most tragic twists of fate, deliberately stabs his own daughter to death upon her request, in order to prevent further corruption of her virtue.

Why this is even relevant:

Emilia Galotti is a highly notable and highly interesting representative of a watershed moment in European (and especially German) theatre, in that it is a clear sign of a shift from older, established traditions to a new set of theatrical conventions. The institution of the middle-class bourgeois family is firmly established (the mother, father and daughter), as are bourgeois concerns (virtue, marriage into a good family, obedience). Dramatic mechanisms are utilized in order to frankly depict social abuses exacerbated by differences in social status that were prevalent at the time (as well as promoting a more open discussion on them). The common people, to whom the nobility theoretically have an obligation, are given a greater opportunity to scrutinize the failure to uphold such responsibilities and act within a respected set of limits (though the play stops just at the brink of suggesting that regicide is an acceptable answer to this abuse). A young, attractive, virgin heroine (the most vulnerable figure in society) is the central focus, while court officials and nobles are presented as deceitful, petty, lustful, and materialistic wretches.

Most overtly of all, the language has become more lively and realistic than before (meant to simulate actual dialogue as well as somewhat more poetic soliloquies). Metered verse is increasingly abandoned in favour of prose, or a mixture of prose and song. In each of these respects, Emilia Galotti is a very progressive theatrical work given the era in which it was written, and points the way for future dramatists to follow.