Sentence:  Whenever such a mischance occurred—when a waggon-load of valuable merchandise had been smuggled ashore, at noonday, perhaps, and directly beneath their <WSD>unsuspicious</WSD> noses—nothing could exceed the vigilance and alacrity with which they proceeded to lock, and double-lock, and secure with tape and sealing-wax, all the avenues of the delinquent vessel. 
Meaning of the word marked with <WSD> tags:  Not suspicious; not suspecting, unaware ("of" something).