A rich man hires an ex-convict (prisoner, murderer) to spy on his wife because he suspects she's cheating on him; she's blonde. As time goes by they fall in love. He almost caught them together because his dog-tags fell on the bed after making love. They make a plot to rob him and ran away, but the husband comes back earlier from a business trip and after a quarrel he kills her (she is in bathtub laying in blood). The ex-convict, after finding out what happened, kills (or tries to kill — can't recall) husband.
During the movie there are short scenes of a woman laying in bed (or bathtub) and blood transfusion. As movie unravels it turns out that wife collected her blood in order to organize her own false murder (to get rid off husband and ex-convict — husband killed by ex-con and ex-con in prison). So she could runaway with her true lover which is the gardener. They fly away and the movie ends.
Can't remember actors but I think that rich man resembles (Alec Baldwin, Michael Madsen or Steven Seagal) and ex-con (William H. Macy or David Caruso). Those actors only look similar to each other in my memory but I could be wrong.