In the case of Piper v. Moon et al., the Supreme Court of the United States was asked to decide whether a contract between two parties was valid and enforceable. The plaintiff, Piper, had entered into a contract with the defendants, Moon et al., to purchase a tract of land. The contract stated that the defendants would convey the land to Piper upon payment of a certain sum of money. However, the defendants refused to convey the land to Piper, claiming that the contract was invalid. The Supreme Court held that the contract was valid and enforceable. The Court found that the contract was supported by consideration, meaning that both parties had given something of value in exchange for the performance of the other. The Court also found that the contract was not void for lack of consideration, as the defendants had received something of value in exchange for their promise to convey the land. The Court also held that the contract was not void for lack of mutuality of obligation, as the defendants had promised to convey the land to Piper upon payment of the agreed-upon sum of money. The Court further held that the contract was not void for lack of capacity, as the defendants had the legal capacity to enter into the contract. In conclusion, the Supreme Court held that the contract between Piper and Moon et al. was valid and enforceable. The Court ordered the defendants to convey the land to Piper upon payment of the agreed-upon sum of money.

In the case of Piper v. Moon et al., Justice Field delivered a dissenting opinion in which he argued that the lower court had misapplied the law when it found for defendants on their plea of not guilty. He believed that under Missouri state law, plaintiffs were entitled to recover damages from defendants for trespass and conversion of property belonging to them. Furthermore, Justice Field noted that even if there was no actual damage done by defendants' actions, they should still be liable because they acted without legal authority or justification. In conclusion, Justice Field held that plaintiffs were entitled to recover damages from defendants regardless of whether any actual harm was caused by their actions.