He was blackmailed, his children were twice kidnapped and his wife was badly injured in mysterious and dubious circumstances.

dubious 是形容词，由词根 dubi-（表示"怀疑"）和后缀 -ous（表示"具有...性质的"）组成。这个词的基本意思是"可疑的、不可靠的"，常用来形容令人怀疑或不信任的情况或事物。在句中指"情况可疑"，暗示这些事件背后可能有不可告人的原因。