And indeed, as the presence of the falcon comes to play a greater role in the driving action of the film, which is often conveyed in bursts of violence and murder, so too does Sam
Spade's misfortune. His entanglements with law enforcement, gangland thugs
and a murderous seductress, though perhaps karmic to some extent, seem
inextricably to wind their way to Spade's doorstep under the supervision of
the harbinger bird.
A key distinction between the film and the novel comes less from what
might be regarded as a narrative decision than a practical one. The ending
to the novel draws out somewhat longer, as a matter or feasibility one
might deduce. However, it allows Hammett the opportunity to reflect on the
response of the characters around him to this aspect of Spade. The famous
closing line of the film which identifies that statuette ambiguously as
'the stuff that dreams are made of' projects something of a...

This contrasts the end to the novel, where Spade's secretary voices revulsion at his moral detachment (in light
of a treatment of O'Shaughnessey which is consistent through novel and
film) and where Spade and Archer's widow are joined. This is a powerful
moment of the novel which leads to far more insidious speculation about
Spade's motives, withdrawing us from any certainty as to his moral posture.

To the film's credit though, it channels a post-depression darkness
that pervades the universe of the screenplay in a tenor not present in
Hammett's novel. Essentially, though Huston delivers on a screenplay
crafted and even executed twice before, he places it in a world that is
befitting of its time. This is, justifiably and perhaps due in no small
part to its bold loyalty to the novel, the most favorably regarded of the
numerous adaptations of the film.