Murder, my sweet - 1945

Apparently based on a Raymond Chandler book, but I read somewhere that they are very different, so maybe one day I'll read the book too to judge for myself. I hope it's different, because the movie as it is wasn't that great. I didn't like it very much, and I usually like this sort of 'noir' movies.
It starts with Marlowe questioned by the police, accused of murder, and a long flashback takes it back to when it all started, with a man named Malloy asks him, as a private investigator, to find him a girl, Velma, a singer he was in love with but has no idea where she is now. To convince him, he gives him 40 dollars in advance. Marlowe starts investigating, asking the bar owner, but he's sure that woman's hiding something. It appears at this moment that Velma might have died.
Then another man asks him to go with him, as a guard, at a night meeting with maybe a thief, but he's knocked out right away. Coming to his senses again, he sees a girl running away, and then finds his rich client Marriott dead. Apparently he wanted to buy back a necklace that had been stolen, and Ann Grayle tells him it was her father's wife's, and that said wife had given Marriott 8000 dollars to buy it back.
He there meets misterious and dangerous Amthor, then finds himself recluse in a sort of mental hospital for three days, but he escapes and descovers that Amthor and Marriott were blackmailing Mrs Grayle... who turns out to be Velma: a secret she wanted nobody to find out. Now that he knows, she wants to kill him, but her husband Mr Grayle kills her instead. Then Malloy, called Moose, fights with him, out of himself for losing Velma, and the two of them kill each other.
Back to the police interrogation room, Marlowe finishes his story, which will be corroborated by Ann. The police lets him go, and the two of them go away together, and kiss, because after all it might even be a full day since her father killed someone in front of her eyes, and was himself killed in return. You can't expect her to be in a bad mood for that!!! Or to mourn for him more than a day!!!
Boring and uninteresting. Sorry about that.

Dick Powell was Philip Marlowe, Claire Trevor was Mrs Grayle/Velma, Anne Shirley was Ann, Otto Kruger was Amthor, Mike Mazurki was Malloy,