Here in 𝓞, Oliver Cowdery initially wrote “into the hand of the Lamanites”; but then virtually immediately he inserted the plural s inline, giving “into the hands of the Lamanites”. Elsewhere the text has only the plural hands in expressions of the form “fall into the hand(s) of X” (26 times); and of these other occurrences, eight are of the form “fall into the hands of the Lamanites” (like here in Alma 52:10). In fact, in one instance, Oliver made the same error of initially writing hand, although in this case the error was in 𝓟:
For a list of the cases where hand and hands have been mixed up in the history of the text, especially in the manuscripts, see under Mosiah 16:1.
Summary: Accept in Alma 52:10 the corrected reading in 𝓞 of hands (“fallen into the hands of the Lamanites”); usage elsewhere in the text consistently supports the use of the plural hands in the expression “fall into the hands of X”.