As ancient life stories (bioi), the synoptic Gospels exhibit a narrative structure which is biographical, rather than plot-like. Most of the story content is episodic, arranged more or less into a loosely developmental sequence. Birth stories come at the beginning, death and resurrection bring up the rear, and in between we have the early, middle, and later stages of a public career which goes through its own natural growing pains: Jesus appears after John, Jesus gains a following, Jesus selects his lieutenants, Jesus sends them out in pairs, Jesus expands his territory, and then Jesus finally goes too far in the capitol city, whence he suffers the consequences. Alongside this recognizably developmental progression we also interact with the baptizer's political regression: acclaimed, arrested, beheaded. Alongside these two intertwined event sequences, of course, we also find the episodic stuff that befits any good life story, the various scenes, movements, and encounters which add to the story: healings, teachings, explanations, challenges, controversies, and seemingly random itineraries. All in all, therefore, we find some episodes throughout Mark, Matthew, and Luke which do indeed follow logically after related events which came before (if not immediately before) and we find a massive amount of episodic material whose placement seems largely if not entirely arbitrary.
The fact that most of the logical structure is developmental marks these narratives as biographical, as does the fact that most synoptic episodes bear no causal relationship to any other specific episode before or after. Both trends are typical of life stories. In such stories, the overall lack of narrativized causality stands in stark contrast to the typical falling of dominoes ("after this, therefore because of this") which defines most authorial emplotments, whether fiction or non-fiction. Again, this failure to maintain a coherent causality throughout its event sequence is perfectly appropriate for any biographical narrative. As I have noted before, biographies are notorious for not really having a plot.
None of this, however, means that Gospel writers did not infuse their narratives with some degree of emplotment. For instance, the Gospel of Mark famously incorporates a recurring motif ("the messianic secret") which builds suspense while increasing coherence. Other thematic elements add coherence in abstract ways but the suspenseful recurrence of the requested secret-keeping prompts the reader to anticipate forthcoming activity, which lends coherence on the level of action and narrative structure. Likewise, Mark's choice of beginning and ending are elements of emplotment, not merely because they enhance the drama of the presentation but primarily because the selectivity of a start point and end point amounts to an authorial definition about the order of events. John's preaching (at the start) and the centurion's question (at the end) provide particular boundaries for Mark's narrated event sequence.
Arguably, the most significant aspect of emplotment in Mark's Gospel is the dramatic juxtaposition of Peter's confession that Jesus is Lord, followed closely by Jesus's rebuke of Peter. Because these two events surround the revelation that Jesus intends to go die in Jerusalem, the structure provides Mark's life story with a veritable climax, a pivot point between "rising action" and "falling action" in the classical sense. This bit of causal structure does not by itself constitute a plot, per se. Rather, the most we can reasonably say is that Mark's featured imposition of this narrativized climax constitutes a degree of emplotment.
[**SIDEBAR: Incidentally, that Mark's major authorial emplotment was adopted by Matthew and Luke demonstrates that this "climactic point" was important to the early Christian messaging about Jesus. The earliest Gospel audiences were not kept in suspense about Jesus's ultimate fate. Early Christians listening to an early Gospel performance had been told long ago--certainly preceding any public recitation of published literature--that Jesus's public ministry ended with crucifixion and resurrection. Thus, Mark's purpose in providing this aspect of emplotment is transparent. The surprise (and the sales pitch) is not that Jesus will die but that Jesus predicted his death and embraced it, long in advance. The bit of climactic structure is featured so that you may be persuaded that this explanation is true.**]
Furthermore, scholars are reaching and stretching when they cobble together all these bits of emplotment in order to claim that said bits altogether happen to comprise Mark's overall plot. For instance, another brief causal sequence appears when the death of John causes Herod Antipas to seek Jesus, which in turn prompts Jesus to sail over to Philip's territory. However, the coherence of this short chain-reaction does not expand to encompass the rest of Mark's narrative content. In other words, the chain of events around John's death are not contained within a larger chain of events which provides overall coherence.
The bit about John's death is a bit of emplotment. The bit about Jesus's embracing his fate is another bit of emplotment. The start point and end point and stages of career development provide additional bits of emplotment. What we do not find is any consistent thread or a single unified scheme which might incorporate all these bits into one overall chunk of coherence. Moreover, we clearly find reams of episodic material with no specifically causal connections to any of the above.
In conclusion, the synoptic storyline is biographically oriented, sequencing most of its episodic material in ways which seem largely arbitrary, and yet it contains aspects of authorial emplotment. Recognizing a handful of micro-emplotments in Mark's Gospel does not justify speaking of that Gospel as if it possesses any single overarching plot. Just like most narrated life stories, Mark simply does not have a plot. The action in the Gospels is not driven by a sense of all-sufficient "after this, therefore because of this" causality. Rather, the narrated event sequence is sometimes developmental, sometimes arbitrary, and occasionally features a brief chain of reactions directed by causality.
Homer's Iliad and Odyssey can be summarized by their plots. Most Greek dramas can be summarized by their plots. Shakespeare's famous five-act structure is entirely summarizable in terms of its plot. But biographically oriented storylines simply cannot be said to have plots. We can say they convey an event sequence. We can "plot out" (so to speak) the basic points in their storylines. We can talk about the chronological order of narrated events seeming more or less arbitrary until we come upon one of those major developmental progressions. And yes, we can note that handful of micro-emplotted episodes. But that is about as far as we can stretch our analysis in the direction of anything remotely resembling a classical narrative plot.
For all of these reasons, the extent to which some Gospel scholarship continues to speak about the "plot" of the Gospel (and/or incorrectly equates "plot" with "emplotment") demonstrates a dearth of narratological sophistication which should be amended. Perhaps in more ways than one...