An excellent read with some alcohol content and profanity used by antagonists.
Plot
Dr. Elwin Ransom, a Cambridge don, is abducted while trying to perform a good deed, and is taken as a hostage on a journey through space. He and his captors, Weston and Devine, land on the planet Malacandra (which we later learn is the inhabitants' name for Mars), where Ransom unwittingly learns that he is to be delivered to the natives, presumably as a human sacrifice to their gods.
Morality
Morals are clearly defined. One of the antagonists has rather skewed views as to what is moral (i.e. believing that population cleansing and killing off another planet's inhabitants to make room for humans is the right thing to do), but that is clearly pointed out and shown to be wrong.
Spiritual Content
The 'eldil' on Malacandra are what we would call angels and Oyarsa, a key character in the latter part of the book, is the arch-angel of Malacandra. The Young Maleldil is obviously Christ, while His father, mentioned several times, is obviously God the Father. The arch-angel (Lucifer) of our planet is also mentioned.
Violence
When Ransom initially meets Weston and Devine, they are scuffling with a boy in an attempt to kidnap him. They later detain Ransom by force and knock him out with a blow to the head. Weston and Devine shoot several inhabitants of Malacandra.
Drug and Alcohol Content
Ransom is invited to visit and "have a drink" (whiskey, though he never actually tastes it). A joke is made by Devine about a young boy being fond of alcohol, which appears to be true. Weston and Devine are implied to have been smoking both cigars and cigarettes, and Devine is said to be drunk at least twice throughout the course of the tale. Ransom is drugged by Devine to make kidnapping him easier.
Sexual Content
Ransom, Weston, and Devine wear no clothing during the voyage because it's very hot. There are no women around, however, and there's nothing crude about it. Devine says Weston can have relations with some of the native creatures, "if he's so fond of them", though he never does. When Ransom first meets one of the Malacandrian creatures, he believes the belt it is wearing is its genitals. A mountain is described as 'looking like a woman's breast'.
Crude or Profane Language or Content
There are 2 instances of "damn," 1 of "ass" (used to mean "fool"), and 3 of "Who the devil?", "By God!", etc. Also, that's all by the antagonists. None of the protagonists use profanity.
Conclusion
'Out of the Silent Planet' is an excellent beginning to C.S. Lewis' 'Space Trilogy'. The characters are well-introduced, the plot enchanting, and the spirituality fascinating. The contrast between the antagonists' morals and Ransom's is very clear and valuable. The above-mentioned references to drinking and the few instances of profanity do not detract from the values of the book, but rather sharpen the distinction between the antagonists and the protagonists.